Hirsutella sinensis (HS) is a mycelium isolated from the fruiting body of the medicinal mushroom Cordyceps sinensis . This study explored whether HS treatment affects reproductive dysfunction in a high-fat diet (HFD)-induced mouse model and regulates various mechanisms, focusing on oxidative stress, apoptosis, inflammation, and autophagy. Twenty-four C57BL/6J (B6) mice were randomly divided into a standard chow diet (NCD)- or HFD-fed group for 24 weeks. During the final 8 weeks, half of the HFD-fed mice were orally administered HS (HFD + HS). Biochemical markers, including glucose, insulin, triglycerides, and total cholesterol, were assessed, and hormones, including testosterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH), were analyzed. Liver and testicular histology, as well as sperm quality markers such as sperm motility, sperm count, and percentage of sperm with normal morphology, were observed. The activities of the testicular antioxidants superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) and the products of lipid peroxidation, such as malondialdehyde (MDA), were measured. The protein expression levels of apoptosis-, autophagy- and inflammation-related markers were measured. The HFD-fed mice had abnormal sex hormone levels, poor sperm quality, and a destroyed testicular structure, with increased oxidative stress and apoptosis in the testis. HS supplementation in HFD-fed mice attenuated testicular apoptosis by suppressing the Bax/Bcl-xl ratio and cleaved caspase 3 protein expression. The HS-treated mice exhibited improved reproductive function, possibly due to reduced oxidative stress and apoptosis, suggesting that HS has a protective effect against HFD-induced testicular damage. Male mice supplemented with HS exhibited attenuated poor semen quality and reduced testosterone levels brought about by HFD-induced obesity by reducing oxidative stress.