The objectives of this study were to relate concentrations of plasma urea nitrogen(PUN) to conception rate in dairy cows. the relationship between PUN concentration and time postcalving was examined for 11 individual cows. Mean concentration of PUN rose for serveral weeks after calving and then was stable from 7 week. As PUN increased, the rate of conception decreased. Cows with PUN<15 and 15∼19.9mg/dl had the likelihood ratios of conception of 1.33 and 1.67. As PUN increased 20∼22.9 and 23mg/dl, the likelihood ratios decreased to 1.00 and 0.90. Thus, low PUN had a favorable association with conception, whereas high PUN had a negative association with conception.