Since heavy metal dirtiness, which we frequently encounter in environmental pollution causes harmful effects on the organism through biochemical enzyme reactions, in this study, the effects of mercury (Hg+2), copper (Cu+2), and zinc (Zn+2) heavy metal ions, which are common in environmental pollution, on PON (paraoxonase) enzyme activity in muscle tissue of bonito (Sarda sarda) were investigated. In the study, 25 bonito (S. sarda) fish muscle tissues freshly obtained from the Samsun region sea were used. The changes in PON enzyme activity were determined by adding different volumes of heavy metal solutions. PON enzyme activities of Hg+2 heavy metal ion used in different volumes were calculated as 30.9383 U/mLdak, 29.0598 U/mLdak, 26.3799 U/mLdak, 23.9443 U/mLdak, 20.6725 U/mLdak, PON enzyme activities of Cu+2 heavy metal ion used in different volumes were calculated as 19.7949 U/mLdak, 19.4807 U/mLdak 19.1864 U/mLdak, 19.1200 U/mLdak, 18.9037 U/mLdak and PON enzyme activities of Zn+2 heavy metal ion used in different volumes were calculated as 23.8305 U/mLdak, 23.0781 U/mLdak, 22.9073 U/mLdak, 22.4324 U/mLdak, 21.8159 U/mLdak. As a result of these obtained data, activity (%) values were calculated and activity (%) graphs were drawn. As a result of the study, it was determined that increasing concentrations of Cu+2 and Zn+2 heavy metal ions caused a decrease in PON enzyme activity, but there was no statistically significant difference between the different concentrations used. It was determined that increasing concentrations of Hg+2 heavy metal ion inhibited the PON enzyme activity, caused a statistically significant decrease between the activities depending on the different concentrations used (p < 0.05).