Meiotic gynogenesis was optimized in the far eastern catfish, Silurus asotus, using both UV-irradiated heterospecific sperm and thermal shock treatment. Eggs were activated with the sperm of mud loach (Misgurnus mizolepis) which had been irradiated with UV at dose levels ranged from 1,020 to 15,000 ergs/mm2. By examining haploidy incidence and survival of the embryos, the optimal dose for genetic inactivation of the sperm was proven to be 7,020 ergs/mm2. Combination of the initial treatment timing (5 min post fertilization) and duration of cold shock (40 mins at 4℃) yielded 92.4% of matching success. Restoration of diploid states was verified using karyoloical analysis. The sex ratios of offsprings from control crosses and gynogenetic groups were different : control group showed no deviation from 1:1 ratio (P>0.05), while gynogenetic groups displayed all femaleness (P<0.05). This results indicates that genetic sex determination of far eastern catfish is based on the XX-XY system (female homogamety), and this advance also has implication on the production of genetically improved all-female far eastern catfish stock.