Koo's second wife, Tang Pao-yueh "May" (; c. 1895–1918), was one of the illegitimate daughter of the former Chinese prime minister Tang Shaoyi and a concubine Mai-Mai Sze. Their marriage took place soon after Koo's return to China and divorced his first wife in 1912. She died in the US during the 1918 Spanish flu pandemic. They had two children: a son, Teh-chang Koo (1916–1998), and a daughter, Patricia Tsien (1918-2015),.
