This study was carried out to investigate environmental effects on certain economically important genetic traits in swine. Data from the 12,402 performance records obtained at the Korean Second Swine Test Station from the year 1990 through 1997 were used for the study. The statistical analyses were made on effects of breed, sex, farm region, parity, litter size, year and season of birth. The average daily gain of Duroc was superior to those of Landrace and Yorkshire. The backfat thickness of Duroc was thicker than those of the other two breeds (P$lt;0.01). The selection indices in Landrace and Yorkshire were bigger than those of Duroc in both ways of index calculation. The effects of birth year on backfat thickness, feed efficiency and the days to 90㎏ exerted gradual progress(P$lt;0.01). Most of the growth traits of pigs born in fall or winter were superior to those of pigs born in spring or summer(P$lt;0.01). The effects of litter size showed significant differences in all of the traits studied.