Oocyte maturation disorder and decreased quality are the main causes of infertility in women, and granulosa cells (GCs) provide the only microenvironment for oocyte maturation through autocrine and paracrine signaling by steroid hormones and growth factors. However, chronic inflammation and oxidative stress caused by ovarian hypoxia are the largest contributors to ovarian aging and GC dysfunction. Therefore, the amelioration of chronic inflammation and oxidative stress is expected to be a pivotal method to improve GC function and oocyte quality. In this study, we detected the protective effect of chitosan oligosaccharides (COS), on hydrogen peroxide- (H2O2-) stimulated oxidative damage in a human ovarian granulosa cell line (KGN). COS significantly increased cell viability, mitochondrial function, and the cellular glutathione (GSH) content and reduced apoptosis, reactive oxygen species (ROS) content, and the levels of 8-hydroxy-2′-deoxyguanosine (8-OHdG), 4-hydroxynonenal (4-HNE), hypoxia-inducible factor-1α (HIF-1α), and vascular endothelial-derived growth factor (VEGF) in H2O2-stimulated KGN cells. COS treatment significantly increased levels of the TGF-β1 and IL-10 proteins and decreased levels of the IL-6 protein. Compared with H2O2-stimulated KGN cells, COS significantly increased the levels of E2 and P4 and decreased SA-β-gal protein expression. Furthermore, COS caused significant inactivation of the HIF-1α-VEGF pathway in H2O2-stimulated KGN cells. Moreover, inhibition of this pathway enhanced the inhibitory effects of COS on H2O2-stimulated oxidative injury and apoptosis in GCs. Thus, COS protected GCs from H2O2-stimulated oxidative damage and apoptosis by inactivating the HIF-1α-VEGF signaling pathway. In the future, COS might represent a therapeutic approach for ameliorating disrupted follicle development.