Pathological examination of the immune organs, pedal pad swelling experiments, alpha-acetate naphthalol esterase stain for peripheral blood lymphocyte, spleen cell interleukin-2 (IL-2) release, in vitro concanavalin-A (Con-A)-induced lymphocyte proliferation test were carried out to study the effects of dimethylformamide (DMF) on the animal immune organs and its cellular immunotoxicity. Results showed DMF could lower the relative weight of spleen and thymus and decrease significantly reaction value of pedal pad swelling mediated by sheep red blood cell in mice. Exposure to DMF through subcutaneous injection and gastric instillation could cause the decrease of peripheral ANAE-positive lymphocyte in different species of animals. Exposure to DMF at doses of 1/10 and 1/160 LD50 could significantly cause decrease of IL-2 release. Tests in vitro showed DMF with doses of 10-150 mmol/L could inhibit significantly lymphocyte proliferation induced by Con-A. It suggests DMF has effects on cellular immunotoxicity in mice.