The changes of actomy osin( AM) in cultured and wi ld praw ns by thermal tr eatment w ere studied biochemica lly and phy sica lly. The experimental result s showed that the so lubility and C a 2+ -ATPase a ct iv ities o f AM decr eased with the increase o f tempe rature, in w hich the cultured pr awn. s decreased mo re rapidly than tho se of the w ild. s. Ther e w as a sma ll dif ference in a ct iv ity between Mg2 -ATPase and Ca2 -ATPase . The ATPase of cultured praw n w as ent irely deactiv ated a t 50 e , w hile the w ild at 55 e . The number o f unmasked-SH gro ups g radually incr ease d f rom 20 to 40 e , then decreased. The hydropho bicit ies of AM incr eased signif ica nt ly w ith the elev at ion o f temperature abo ve 40 e . No change o f ATP sensit ivit ies at no rma l temperature, but decreased rapidly f rom 35 e . All the ment io ned indices in AM were great ly af fected in the temper ature r ang ing f rom 30 to 40 e , howeve r, AM o f cultured praw n w as less stable than the w ild o ne.