This study was carried out to get a fundamental information for improvement of reproductive performance in gilt. We investigated the effects of breeds on body weight, age, body length, wither`s height, girth and backfat thickness, and the serum concentrations of estradiol-17b, cortisol and progesterone at first estrus and mating of gilts. A total of 47 guts of Duroc, Landrace and Yorkshire, produced at Livestock Experiment Station, Chungnam livestock sanitation research institute from 2000 through 2002, were used for this experiment. Body weight, age and girth of Duroc at first estrus and mating were higher than those of Landrace and Yorkshire. There were no differences on body length among the three breeds at first and mating. Wither`s height of Duroc and Yorkshire at first estrus and mating was higher than that of Landrace. Backfat thickness of Yorkshire was thinnest among the three breeds at first estrus, but there were no differences on backfat thickness among the three breeds at first mating. Serum estradiol-17.8 concentration of Landrace(45.0 pg/ml) at first estrus was higher than that of Yorkshire(27.4 pg/me) and Duroc(21.8 pg/me), but there were no differences on estradiol-1719 concentration(from 18.5 to 31.9 pg/ml) among the three breeds at first mating. Serum cortisol concentration of Duroc at first estrus and mating was higher than that of Landrace and Yorkshire. There were no differences on serum progesterone concentration among the three breeds at first estrus and mating of gilt.