The PZL.4 was a high-wing cantilever monoplane of metal construction, with closed cab and three engines. The fuselage was rectangular in cross-section, made of duralumin and covered with duralumin sheet. The two-spar wings and tailfins were covered with Wibault-pattern ribbed duralumin sheet. The wings had squared-off wingtips. A crew of two (pilot and mechanic), were accommodated in front, before the wing, equipped with twin controls. Behind and slightly below under the wing, there was a cabin for 10 passengers in three compartments in the fuselage. The cabin had wide rectangular windows, sloped outwards for a better view, and door on the left side. The cabin had places for a baggage behind it and below a floor.
