Abstract: The mechanism of cryoprotection of fish spewn by dimethylsulfoxide(DMSO)lie is itsfast penetration into the sperm and increase of the osmotic pressure of the sperm, Results ofthis study showed that the osmotic pressure of the spenn increased in direct proportion to thetreatment time and concentration of DMSO,Before cryopreservation, when the spem wastreated with 14 % DMSO for 5-7h,its osmotic pressure rose to a peak level of 1538mOsm / L,which was five times higher the level under natural conditions.After thawing,theosmotic pressure of the sperm was still maintained at 1025 mOsm / L,or three times the levelunder natural conditions.When the DM SO concentration increased to 22% prior tocryopreservation, sperm osmotic pressure rose to 1538 mOsm / L immediately, and wasmaintained at 1367 mOsm / L after thawing. After thawing,the spenn osmotic pressure was 171-513 mOsm/ L lower than beforethawing.The survival rate after thawing was highest when the osmotic pressure of the spennprior to cryopreservation was 1025-1367 mOsm / L. As the spenn osmotic pressure afterthawing was 3-4.5 times higher than that under natural conditions,it was necessary to acti-vate the speml with 1.0-2.0% NaCl to achieve higher survival rate.The relationship between sperm osmotic pressure(Y)and DMSO concentration(X)was:Y=0.148X+1245,r=0.898(Osmotic pressure before thawing)and Y=0.136X+0.641,r=0.968(Osmptic pressure after thawing)