structural:expansion, quality:corruption
War crimes

Italian military forces used between 300 and 500 tons of mustard gas to attack both military and civilian targets, despite being a signatory to the 1925 Geneva Protocol banning the practice. This gas had been produced during World War I and subsequently transported to East Africa. J. F. C. Fuller, who was present in Ethiopia during the conflict, stated that mustard gas "was the decisive tactical factor in the war." Historian Walter Laqueur estimates that up to one-third of Ethiopian casualties of the war were caused by chemical weapons.

The Italians claimed that their use of gas was justified by the execution of Tito Minniti and his observer in Ogaden by Ethiopian forces. However, the use of gas was authorized by Mussolini nearly two months before Minniti's death on 26 December 1935, as evinced by the following order:

Rome, October 27, 1935. To His Excellency Graziani. The use of gas as an ultima ratio to overwhelm enemy resistance and in case of counter-attack is authorized. Mussolini.

After Minniti's death, the order was expanded to use of gas "on a vast scale":

Rome, December 28, 1935. To His Excellency Badoglio. Given the enemy system I have authorized Your Excellency the use even on a vast scale of any gas and flamethrowers. Mussolini.

Military and civilian targets were gas bombed and on 30 December, a Red Cross unit was bombed at Dolo and an Egyptian ambulance was attacked at Bulale; a few days later an Egyptian medical unit was bombed at Daggah Bur. There were more attacks in January and February, then on 4 March 1936, a British Red Cross camp near Quoram appeared to be subject to the most deliberate attack of all, when low-flying Italian aircraft crews could not have missed the big Red Cross signs. Mustard gas was also sprayed from above on Ethiopian combatants and villages. The Italians tried to keep their resort to chemical warfare secret but were exposed by the International Red Cross and many foreign observers. The Italians claimed that at least 19 bombardments of Red Cross tents "posted in the areas of military encampment of the Ethiopian resistance", had been "erroneous".

The Italians delivered poison gas by gas shell and in bombs dropped by the Regia Aeronautica. Though poorly equipped, the Ethiopians had achieved some success against modern weaponry but had no defence against the "terrible rain that burned and killed".

In general, historians concluded that the use of chemical weapons was effective and devastating to morale and manpower, though some disagree and argue that they had negligible effect in battle. Historian Angelo Del Boca condemned the use of gas, but argued that it had only a minimal effect on Italian war aims. An analysis by the Stockholm International Peace Research Institute argued that the use of chemical weapons shifted the war in favor of the Italians, and dealt a major blow to Ethiopian morale.

American and British military analysis came to similar conclusions. The US military concluded that "Chemical weapons were devastating against the unprepared and unprotected Ethiopians." British Major General J. F. C. Fuller, assigned to the Italian army, noted that "In place of the laborious process of picketing the heights, the heights sprayed with gas were rendered unoccupiable by the enemy, save at the gravest risk. It was an exceedingly cunning use of this chemical."

Haile Selassie in his report to the League of Nations described it:

....Special sprayers were installed on board aircraft so they could vaporize over vast areas of territory a fine, death-dealing rain. Groups of 9, 15, or 18 aircraft followed one another so that the fog issuing from them formed a continuous sheet. It was thus that, as from the end of January 1936, soldiers, women, children, cattle, rivers, lakes, and pastures were drenched continually with this deadly rain. In order more surely to poison the waters and pastures, the Italian command made its aircraft pass over and over again. These fearful tactics succeeded. Men and animals succumbed. The deadly rain that fell from the aircraft made all those whom it touched fly shrieking with pain. All those who drank poisoned water or ate infected food also succumbed in dreadful suffering. In tens of thousands the victims of Italian mustard gas fell.

Ethiopian troops used Dum-Dum bullets, which had been banned by declaration IV, 3 of the Hague Convention (1899) and began mutilating captured Eritrean Askari (often with castration) beginning in the first weeks of war. Some hundreds of colonial Eritrean Ascari and dozens of Italians suffered these amputations, often done before death as allegedly happened to 17 Italian workers emasculated in Gondrand in February 1936.