The present study was determined the effect of combined mycotoxins caused by Aflatoxin and zearalenone exposure on reproductive performance and their relation to the incidence of ovarian cysts in dairy cattle. The present study used 28 lactating cows kept at dairy farm in Dakahlia governorate. Cows were classified into two groups First group (10 cows) were received ration where the percentage of aflatoxin and zearalenone not exceed permissible limit which is (5 ppb and 200 ppb respectively) and show normal estrous behavior and have mature large follicles >22mm<25mm in diameter and have corpus luteum. The second group (18 cows) received ration containing aflatoxin which found exceed permissible limit (19.7 ppb) and zearalenone which was present at high levels (400 ppb), these cows exhibit“constant" estrus (nymphomania), excessive vaginal discharge, until day 45 postpartium and have ovarian cysts based on the presence of follicular structure (≥25 mm in diameter) with anovulation and the absence of corpus luteum. Blood samples was collected from each cow around 45 days postpartium for evaluation of serum progesterone (P₄), estrogen (E₂), Luteinizing hormone (LH), triiodothyronine (T₃), thyroxin (T₄), prolactin (PRL) total protein, calcium, inorganic phosphorus, Liver enzymatic activities alanine aminotransferase (ALT) and aspartate aminotransferase (AST) immunologlobins (IgG, IgM, IgA). The results of hormonal assay showed significant increase (p < 0.05) in levels of prolactin and estrogen, while levels of LH, progestone, T3 and T4 showed significant decrease (p < 0.05) in cows received contaminated ration with zearalenone and aflatoxins in compared with control one. Regarding to results of biochemical and immunological parameters revealed a significant increase (p < 0.05) in enzymatic activities (AST), (ALT), while total protein, calcium, inorganic phosphorus and immunological parameters (IgG, IgM, IgA) showed significant decrease (p < 0.05) in cows received contaminated ration with zearalenone and aflatoxins compared with control one. Our results using transrectal ultrasonography revealed that mean diameter of follicular cyst was 42.3±3 mm of cows received contaminated ration with zearalenone and aflatoxins while mean diameter of mature follicles was 22.1±1.7 mm of control cows.       We concluded that zearalenone have been shown to competitive bind to oestrogen receptors and affect reproductive performance generating hormonal imbalance inducing cell toxicity, immunosuppression due to the combined effect of aflatoxins which may predispose cows to the incidence of ovarian cysts