It has estimated that MID100(100% monkey infected dose) of SIVmac251 was 32 TCID andSIVmac239 was more than 320 TCID. Three monkeys inoculated with SIVmac251, two monkeysSIVmac239 and seven monkeys SIVmac251 2 MID100 were infected pefectly. All infected monkeysappeared generalized lymphopathy, plasma viremia and antibody response regularly. The pathological examination of lymph nodes and spleens in seven Rhesus and two cynomolgus monkeysshowed infectious changes. It is quite obvious that the symptoms an sign, Pathological histologicalchanges, and viremia and antibody response of infected monkeys were caused by SIVmac251 orSIVmac239 strain. So above strains could be used to evaluate the effect of anti - AIDS drugs inmonkey test.