Biological ammonia removal system have been used conventionally for the seawater fish farming. But this process requires long hydraulic retention times and large area. Also it has a trouble of NO3-N accumulation in the system. Therefore, this study was conducted to find out the feasibility of effective nitrogen removal efficiency in the sea water fish farming system by electolysis. As the result, electrolysis system showed a good ammonia and nitrate nitrogen removal and E. coli sterilization efficiencies. Because of the high salinities in the seawater for electron transfer, electrolysis is an effictive water treatment process for seawater fish farming. The relation among ammonia removal efficiency, hydraulic retention time (HRT) and electric wattage (watt) with 10 mm electrod distance isas follow ; log [$NH_4^$+-N(%)]=0.431log(HRT(sec)$ imes$Watt)+0.88(r=0.950) And the relation between ammonia removal efficiency and residual chlorine concentration in the seawater is as follow; $$NH_4^+-N(%)=48cdotlog[Residual;chlorine(mg/ell)+28(r=0.892)$$