This study was conducted to determine the main effects of year, month, sire and parity on certain reproduction and lactation traits on the basis of the data obtained from 1,510 head of Holstein cows at National Animal Breeding Institute from 1971 to 1981. The results obtained in this study are summarized as follows; 1. The conception interval and number of services per concetption were 124.10 days and 2.19 times, respectively. The effects of year, month and sire on the above traits were significant. 2. The birth weight and gestation length were 42.20kg and 281.52 days, respectively. The effects of year, month and parity on the birth weight, and year, sire and parity on gestation length were significant. 3. The yields of milk and milk fat in 305 days, and the fat percent were 4937.05kg, 174.43kg and 3.56%, respectively. The effects of year, month, sire and parity on the above traits were significant. 4. The peak yield and days reaching the peak yield were 26.46kg and 49.17 days, respectively. The effects of the sire and parity on above traits were significant.