Previous research indicates that high blood urea nitrogen (BUN) concentrationsare associated with decreased fertility in lactating dairy cows.This experiment was done to evaluate the effects of equine chorionic gonadotropin (eCG) administration (with or without eCG) on fertility of lactating dairy cows with different levels of BUN subjected to fixed-time artificial insemination (FTAI).Ovulation was synchronized in all cows using Presynch-Ovsynch program and start 37 days post parturition(pp). Blood samples were collected on days 50-55 pp to assess BUN and cows were classified as with high urea when BUN was 20< ng/mL(n=64); otherwise, they were classified as cows with optimal urea when BUN was >10 and <15 (n=62). Within each group, cows were assigned randomly to receive either 600 IU eCG concurrent with PGF2a treatment of the Ovsynch protocol (treatment cows)or with no further treatment (control cows). Blood samples were collected on Days 0 and 5 after FTAI to evaluate the effect of eCG administration on synchornization and plasma concentration of P4. Pregnancy diagnoses were performed by ultrasound. No treatment effects were detected for Pregnancy per AI at Days 30. However, P/AI at Days 30 was not affected by treatment with eCG but P/AI at 60 days post-AI in cow with high BUN levels in control group was less and differed significantly than treatment group with optimal BUN (OR=4.722; P=0.016). This differ significant, P/AI at 60 days post-AI no observed in cow with high BUN that treatment with eCG. P4 concentrations on Days 5 differed significantly between treatments and control group in both levels of BUN concentration. Inclusion of eCG in ovsynch protocol increased progestron concentrations in early time of luteal phase after AI. The use of eCG in ovsynch protocol will improve reproductive efficiency in dairy cows with high levels of BUN.