Objective To study the chronic toxicity and carcinogenicity of 95% isocarbophos and to provide its no observed adverse effect level (NOAEL). Methods Four hundred and eighty male and female SD rats were divided into 4 groups and fed with foods containing 0, 0.6, 6 and 30mg/kg isocarbophos respectively for 2-years. The daily behavior, body weight, food consumption, blood biochemistry, clotting time, cholinesterase activity, gross anatomy and histopathology, and the incidence of tumors were examined and analyzed. Results Activities of cholinesterase were significant decreased in some females (at the 6, 18, 24 month of the 30mg/kg group) and males (at the 6, 12, 18, 24 month of the 6 mg/kg and 30mg/kg groups). There were no any significant changes at any level of Isocarbophos on any other parameters including the incidence of tumor in any organ or tissue. Conclusion The NOAEL of isocarbophos were 0.486 and 0.037 mg/(kg BW?d) for female and male respectively, and isocarbophos is non-carcinogenic under the conditions of the study.