Abstract: Biochemical characters and protein compositions of intermediate filament (IF) -nuclear matrix (NM) system of vegetative- and resting-cell of Tachysoma pellionella were studied by the method of serial selective extraction,diethylene glycol distearate (DGD) embedment and emebedment-free electron microscopy,and SDS-PAGE.The result shows that in the vegetative cell,the IF,with diverse density in different regions,occurs in the cytoplasm;50 nm thick and thin-layer-shaped lamina,in the periphery of nucleus;the NM is composed of a more densely arranged filament network.The same kind of network also exists in the resting cell,as well as in the middle-level layer of cyst wall,but presents more compact compared with the similar structure of vegetative cell,and this phenomenon may refer to the comprehensive contraction in the course of encystment.The result of SDS-PAGE shows that protein composition of this system has changed notably when the cyst is formed,of which,part of the proteins have been preserved and part lost,and some new and distinct proteins occur.The following conclusions can be obtained:the IF-NM system is a stable structure in both vegetative- and resting-cell;changes of IF-NM system and protein composition after encystment reveal that gene expression of resting cell is different from that of vegetative cell.