Abstract: Background and Objective: Inhibin is an intra-ovarian regulator of the ovarian cycle by modifying the action of the gonadotropins regulators of the ovarian cycle where Follicle Stimulating Hormone (FSH) secretion from anterior pituitary gland is dependent on the secretion of ovarian inhibin, estradiol or both of them. The present study was conducted, in cycling female rats to investigate the effect of antisera against steroid-free bovine follicular fluid (S-FBFF) or inhibin-free S-FBFF on hormones profile that influenced in reproduction. Materials and Methods: Follicular fluid was aspirated from bovine mature follicles, centrifuged and treated with activated charcoal. S-FBFF was divided into 2 parts: first part was used for immunization of adult male rabbits against S-FBFF (for obtaining inhibin antiserum; S-FBFF antiserum) and second part was treated with anti-inhibin before immunization of adult male rabbits against S-FBFF (for obtaining activin antiserum; IS-FBFF antiserum). After 5 injections (a week interval), blood was collected, centrifuged and antiserum was obtained. One hundred virgin cycling female rats (aged 65 days and weighted 150-170 g) were randomly assigned to five equal groups and i.p injected with 100 μL of normal saline (control), S-FBFF antiserum at proestrus (T1), IS-FBFF antiserum at proestrus (T2), S-FBFF antiserum at metestrus (T3), or IS-FBFF antiserum at metestrus (T4). At estrus phase, 10 females from each group were euthanized and blood samples were obtained for assessment of serum follicle stimulating hormone, estradiol, growth hormone and insulin-like growth factor-1 and -2 concentrations. One way analysis of variance (ANOVA) and Newman Keuls were used to test all groups unpaired values. Results: The results demonstrated significant increase of serum concentrations of FSH, estradiol-17β, GH, IGF-1 and IGF2 in T3 group among experimental groups, whereas the lowest (p<0.05) level was recorded by T4 group compared with control. Conclusion: In conclusion, inhibin immunoneutration can be inducted by the use of S-FBFF antiserum at metestrus, which has potent effect on reproductive potency in female rats.