The objective of this study was carried out to determine the influence of extenders on AST activity during preservation of boar semen. A total of 37 ejaculates were used for this study. The semen was diluted in dilution ratio 1+8 in extenders Androhep (A), Safecell Plus (SCP) and SUS and was stored at a temperature of 17°C. AST activity was evaluated at 24h, 96h, 168h and 240h after semen dilution and 24h, 48h, 72h and 96h after thawing. The total mean value of the AST activity was 72,69, 89,52, 84,40 mU/109 spermatozoa in A, SCP and SUS, respectively. There were found significant differences between A and SCP extender. Significant differences in the AST activity where noted at 96h vs. 168h and 240h storage time in SCP. The gradual increased the AST activity was observed at all extenders during storage time where total the highest difference was after 96h vs. 168h.The mean values of the AST activity after thawing were 128,27 mU/109 in A, 141,99 mU/109 in SCP and 118,44 mU/109 in SUS. Significant differences in the AST activity where noted SCP and SUS extender. In conclusion, the results of this study showed gradual increase in the AST activity indicating the membrane damage of spermatozoa during storage time. The effect of extenders on the activity of AST was significant during storage time after dilution and after thawing.