TnIAP, which can inhibit apoptosis and was cloned from Tn-5B1-4 cells, was highly expressed in Tn-5B1-4 cells. However，SDS-PAGE and Western blot analysis indicated that only small part of recombinant protein was soluble, which was different from the record that most recombinant protein expressed in insect cells were soluble. Activity assays demonstrated that recombinant soluble TnIAP could inhibit the cleavage of Ac-LEHD-AFC by caspase-9 and the activation of HEK293 cytosolic extracts by caspase-9 from cleaving Ac-DEVD-AFC. This result gave the further evidence that the molecular mechanism of apoptosis is evolutionarily conserved through insects to mammals.