Abstract: To investigate the differences of the major chemical composition of silkworm and tussah pupa and tussah pupa in the progress of hatch,gas chromatography mass spectrometry( GC-MS) was employed to analyze their fatty acids and free amino acids.9 fatty acids were obtained from both silkworm and tussah pupa.Polyunsaturated fatty acids accounted for 74.7% of the total fatty acids of tussah pupa and 60.9% of silkworm pupa while the content of stearic acid and palmitic acid in silkworm pupa was higher than that in tussah pupa. Alanine was the highest( 34.9%) amino acid in silkworm pupa,and in tussah pupa proline( 37.5%) and alanine( 20.5%) were the most abundant amino acids. During the hatch of tussah pupa,content of most of the detected fatty acids were decreased and a few of them were increased slightly at the moth stage,suggesting the changes of energy utilization in the process.Changes of amino acids were more complicated than that of fatty acids. Content of free amino acid was found higher at the beginning of the hatch than that of later stage.The results showed that growth stage and the process should be considered in possible industrial development.