Rhodopseudomonas sp. was immobilized in three supports(agar, k-carrageenan, and PVA) in order to remove nitrate in wastewater coming from fish farm. Among them 3% agar was the most suitable support when denitrification rate and bead durability were tested. Optimum bead size was 4mm-diameter when the substrate transfer into the bead and shear stress for bead were considered, and optimum cell loading was 25mg dry $cells/cm^2$gel gel. Ethanol was the best as a carbon source, and optimum C:N ratio, temperature and pH were 1.5:1, $31^{circ}C$,, and 6, respectively. Under these conditions the maximum denitrification rate in synthetic wastewater was $$345{MU}{ell};N_2/Cm^3 gel{cdot}hr;and that in modified MYC medium was 450{MU}{ell}};N_2/Cm^3 gel{cdot}hr $$.