Abstract Disclosure: H. Kelestimur: None. Z. Oz: None. M. Ozdede: None. I. Serhatlioglu: None. N. Kaya Tektemur: None. E. Kacar: None. Purpose: Asprosin is a novel glucogenic and orexigenic hormone produced by the fibrillin 1 (FBN1) gene that is secreted by white adipose tissue during fasting. Fibrillins (FBNs) are structural and signalling proteins found mainly in the ovarian stroma, tunica albuginea and theca layers. The aim of this study was to determine the effects of asprosin on ovarian tissue in the female rats. Materials and methods: Twenty-four female Sprague-Dawley rats were randomly divided into 2 groups (n=12) as control and asprosin. Asprosin and control groups were given intraperitoneal saline at doses of 500 ng/kg and 1 ml/kg, respectively, at 14.00 every day for eight weeks. After the application, decapitation was performed, and the rapidly removed ovarian tissues were placed in a 10% formaldehyde solution for fixation. Formalin-fixed ovaries were dehydrated in a graded alcohol series and graded ethanol, respectively After that, all tissues were embedded in paraffin wax. The ovaries were cut into 5-µm sections and stained with hematoxylin and eosin (H&E) and also Masson trichrome staining. Ovarian follicular reserve and fibrosis were evaluated by light microscopy. The follicles were histologically classified as primordial, primary, secondary, and Graaf and all follicular structures were counted in each section. The fibrosis was evaluated with Masson’s trichrome staining and scored from 0 to 3 semi-quantitatively (0 = no fibrosis, 1 = low fibrosis, 2 = intermediate fibrosis, 3 = severe fibrosis). Results: In the asprosin group, unlike the control group, occasional congestion was observed in the vessels located in the ovarian medulla. Apart from this, no histopathological changes were found. An increase in fibrosis was detected in the ovarian sections of the asprosin group when compared to the control group (p = 0,035). In the light microscopic evaluation of the ovarian sections of the rats in the asprosin group, the primary and secondary follicle numbers were significantly higher than those in the control group (p = 0,008 and p = 0,047 respectively). However, the difference between the control and asprosin groups in terms of the primordial follicle, Graafian follicle and corpus luteum numbers were not statistically significant. Conclusion: Our results have shown that chronic asprosin administration causes an increase in the number of primary and secondary follicles, suggesting that changes in ovarian steroidogenesis and folliculogenesis depending on the application may lead to positive effects on female fertility. Keywords: Asprosin, adipokine, ovarian follicle. Acknowledgement: This study was supported by TUBITAK (Project: 220S744). Presentation: Friday, June 16, 2023