Experiments in lab indicated that the persistence of Bt insecticidal crystal protein (BICP) in soil and its effects on soil phosphatase activity were different between forms of BICP introduced into the soil.In the first treatment of the experiments,Bt was applied directly into the soil with results showing that BICP concentration in the soil increased gradually along with the incubation time and reached the peak value on D15 and then decreased.On D30 the concentration of BICP was almost the same as at the initial stage after the application.In the second treatment,Bt cotton tissues were used.The results showed that BICP concentration in soil decreased along with the incubation time.There was a rapid decline at the initial stage of the in cubations and the trend leveled off in the middle and late stages.On D56 of the incubation,BICP in soil was at 44.7% (ZK) and 56.1% (GK) of the initial values.In the third treatment,Bt cotton was planted in pots.Analysis of the soil showed that during the whole growth period,the concentration of BICP in the rhizospherice soil of Bt cotton was significantly higher than that of non Bt cotton.The treatment with Bt and Bt cotton tissues showed a trend of the soil phosphatase activity being higher than that in CK.But the phosphatase activity in the rizhospherice soil of Bt cotton was lower than that of non-Bt-cotton.Whatever forms of BICP were introduced into soil,the difference in soil phosphatase activity between treatments different in BICP concen tration treatment was significant.