Colorectal cancer remains one of the leading causes of cancer-related mortality both in Japan and worldwide. Oxaliplatin (L-OHP) is a key chemotherapeutic agent used in the treatment of colorectal and other malignancies; however, its clinical use is often limited by the development of oxaliplatin-induced peripheral neuropathy (OIPN). In this study, we investigated ergothioneine (EGT), a natural antioxidant abundant in mushrooms, for its potential to mitigate OIPN without compromising the antitumor efficacy of L-OHP. Using the SH-SY5Y neuroblastoma cell line and differentiated neurons, we assessed the effects of EGT on L-OHP-induced apoptosis, oxidative stress, and axonal degeneration. We further evaluated whether EGT interferes with the anticancer activity of L-OHP using cultured cancer cell lines and a tumor-bearing mouse model. EGT suppressed L-OHP-induced apoptosis in neuronal cells and preserved axonal structures in differentiated neurons. Importantly, EGT had no adverse effect on the antitumor efficacy of L-OHP, as evidenced by unchanged cancer cell proliferation, tumor volume, and body weight in treated mice. These findings suggest that EGT may be a promising adjuvant for preventing OIPN while maintaining the therapeutic benefits of L-OHP.