To understand the relationship between the contents of proteins and free amino acids and the infection of Beauveria bassiana.Changes in the contents of proteins and free amino acids in haemolymph of Apriona germari larvae infected by B.bassiana were detected.The result showed that the content of proteins increased to the maximum in 3 days after inoculation,indicating the proteins and enzymes could be produced for the immunologic responses,and then declined.By using the polyacrylamide gelelectrophoresis(PAGE)technique,the change in protein composition in Apriona germari larvae infected by Beauveria bassiana was analyzed.The result showed that the band number increased after inoculation.There were significant differences in the band widths and staining intensities.The results of amino acids analysis showed that there were abundant necessary amino acids for the strain’s growth in A. germari larvae bodies,thus B. bassiana showed a high virulence to A. germari larvae.The content of free amino acids decreased in 24 h after inoculation,suggesting that the B. bassiana invaded into the insect body absorbed some amino acids from the blood as nutrition.The content of free amino acids had no further changes from 24-72 h,and then increased sharply in 96 h and 120 h probably because of gradual loss of immunoregulation,destroy of tissue and disintegration of proteins.Before dead of the infected A. germari larvae,the contents of different amino acids changed differentially,suggesting that different growth phases of the isolate needed different amino acids.