The objective of the present study was to evaluate the relationships among milk urea nitrogen (MUN) and other factors with the probability of conception in dairy cows. A total of 713 dairy herds and 10,271 dairy cows were included in the study. Logistic regression was used to determine the effects of MUN, milk production, lactation number, and breeding season on the probability of conception for each of three services. Within herds, MUN displayed a slight negative association with probability of conception at first service. In among-herd regression analysis, there was no effect of MUN on probability of conception. These results suggest that MUN may be related to conditions affecting reproduction of individual cows within a herd. Diet formulation usually would affect MUN equally among all cows at a similar stage of lactation in a herd. Since there was no effect of MUN among herds, diet formulation to meet the protein requirements did not appear to affect conception rate.