This study was conducted to investigate effects of supplementing two doses of quebracho tannins (QT; 100 or 200 g/cow/d; QT100 or QT200) pre and post parturition to thirty Holstein dairy cows on Dry Matter Intake (DMI), milk yield and composition, blood metabolites and reproductive performance for 12 weeks. There were no significant changes in DMI due to QT at transition period of dairy cows. QT supplementation at either level decreased (P 0.05) the total number of ovarian follicles, number of large follicles, diameter of largest follicle, number of small follicles, number and diameter of corpus luteum, and progesterone concentration. The inclusion of QT increased days open and number of services per conception, which consequently decreased conception rate, compared to the control cows. QT100 decreased (P < 0.05) serum total protein, globulin, glucose and triglycerides concentrations as compared with their values in control cows. Thus, the supplementation of commercial QT to dairy cows at their transition period had negative impacts on productive and reproductive performance.