Our objective was to evaluate the relationship between blood urea nitrogen (BUN) near AI and fertility in Holstein cows. Lactating Holstein cows (n = 541) were submitted to a Double-Ovsynch protocol to receive their first timed artificial insemination (TAI). Body condition score (BCS) was evaluated and a blood sample was collected immediately before the last PGF_2α treatment of the Double-Ovsynch protocol. Blood samples were assayed for progesterone (P4) by RIA and BUN concentrations by ELISA. All cows were fed the same TMR diet containing 17.3% CP/kg DM (RDP - 11.72% and RUP - 5.61%) and 1.65 Mcal/kg DM of NEl formulated to meet NRC requirements. Only synchronized cows (P4 < 0.5 ng/mL at TAI) were included in the analyses. Milk production and components were recorded in the first 4 official milk tests. Cows were divided into quartiles based on BUN (Q1 = least BUN; Q4 = greatest BUN). Data were analyzed by logistic regression and ANOVA using the GLIMMIX and MIXED procedures of SAS. Overall, 95% of all cows were considered synchronized. At 32 d after TAI, there was a quadratic effect (P = 0.03) of BUN on P/AI (59%, 48%, 51%, and 59% for Q1, Q2, Q3, and Q4, respectively). Similarly, at 67 d after AI there was a quadratic effect (P < 0.01) of BUN on P/AI (57%, 45%, 45%, and 56% for Q1, Q2, Q3, and Q4, respectively). Pregnancy loss from 32 to 67 d after TAI did not differ (P = 0.27) among quartiles (4%, 7%, 12%, and 5% for Q1, Q2, Q3, and Q4, respectively). Mean BCS did not differ (P = 0.74) among quartiles (2.96, 2.93, 2.91, and 2.92. for Q1, Q2, Q3, and Q4, respectively). Average energy corrected milk did not differ (P = 0.38) among quartiles (48.4, 48.1, 48.5, and 48.3 kg/d for Q1, Q2, Q3, and Q4, respectively); however, milk protein % was greater (P < 0.01) for Q1 and Q2 cows and least for Q3 and Q4 cows (3.09, 3.06, 2.99, and 2.98, for Q1, Q2, Q3, and Q4, respectively). Thus, there was a quadratic effect of BUN near TAI on P/AI at 32 and 67 d after TAI, and milk protein % decreased as BUN concentration increased. Supported by USDA NIFA Hatch project 1006519