In this study the effects of salinity on the electrocardiogram and some of blood serum minerals in grass carp were investigated. For this purpose, grass carp were exposed to concentrations of 4, 8 and 12 g L^-1 salinities and electrocardiogram of all fish was recorded. Blood samples were also collected from all fish and serum minerals were measured. Our results indicated that mineral level in the studied groups was significantly different. The average of heart rate per minute in control group and 4, 8 and 12 g L^-1 were 10.15, 10.06, 12.17 and 7.79 beat per min, respectively. In 8 g L^-1 group only the average of QT and ST segment decreased significantly in comparison with the control group (p < 0.05). In 12 g L^-1 group the average of heart rate per minute decreased significantly in comparison with 8 g L^-1 group (p < 0.05) and no difference in the average of heart rate per minute was observed in all groups. The average of RR, PT and ST segment in the 12 g L^-1 group were significantly more than the other groups (p < 0.05). The results showed that water salinity level increased to concentrations above 8 g L^-1 can have significant effect on the electrocardiogram and mineral level of blood serum in grass carp. These changes are probably can be considered as one of the causes of impairment of health and death of this fish species in the salinities more than 8 g L^-1 due to ion imbalance and cardiovascular disorders.