The strain, Bacillus amyloliquefaciens BF 7658 possesses the ability to produce protease and some other enzyme as well as ?-amylase. In the experiment, we have observed interference of protease with ?-amylase. If the relative ratio of activity of ?-amylase to protease was 13 : 1, 21 : 1, 27 : 1, the ?-amylase activity of culture incubated at 37℃ for 24h decreased 27.42% and 8.8% respectively. Purified ?-amylase lost the activity about 13—17% by incubation with the protease in 0.2mol/L phosphate buffer pH7.9 at 37℃ for 24h. It is confirmed that protease is one of fatters of unstability of ?-amylase.The pH and temperature affected the stability of both enzymes when cultures were heated in a 60℃ bath for 30 min. Protease activity lost about 90% and ?-amylase activity almost remained unchange.The stability of ?-amylase can be increased by adding 0.01mol/L calcium ion at pH7.0 and treating at high temperature (70℃), but protease activity is inaetivited completely. Different strains and culture conditions also affected the production ratio of ?-amylase and protease. Some strains produced high level of ?-amylase but low level of protease have been obtained.