Unit Ei 1644

Unit Ei 1644 (Japanese: 栄1644部隊), also known as "Unit 1644" was a medical research unit of the Japanese Imperial Army based in Nanjing, China.

Unit 1644 was established after the Nanjing Massacre. It was originally established as an Epidemic Prevention and Water Supply Department (EPWSD) (Boeki Kyusui Bu). It soon became a center for the testing of chemical and biological weapons. It was part of the human experimentation facilities operated by Shiro Ishii.

Unit 1644 conducted tests to determine human susceptibility to a variety of harmful stimuli ranging from infectious diseases to poison gas. It was the largest germ experimentation center in China. Unit 1644 regularly carried out human vivisections as well as infecting humans with cholera, typhus, and bubonic plague.

It is possible that the Japanese, who controlled Manchuria at the time, designated the unit "1644" because it was in this year that the Manchu Dynasty took control of China.