Objective To observe serum uric acid (UA) level of patients with optic neuritis (ON). Methods Thirty-nine patients with ON (ON group), 53 healthy control subjects (control group), 69 patients with multiple sclerosis (MS group) and 51 patients with neuromyelitis optica (NMO group) matched in age and sex were enrolled in the study. In ON group, there were 25 patients with papillitis and 14 patients with retrobulbar type ON. Twenty-eight patients were first time onset while 11 patients were recurrent. The disease duration was less than a year for 28 patients, and over a year for the remainder. Venous blood samples were collected from all individuals in the morning after an overnight fast. UA concentration was measured by the urate oxidaseindirect peroxidase couple assay. Differences of UA concentration were comparatively analyzed among all the groups. UA levels between different genders, different groups, different lesion sites, recurrence and duration of ON were comparatively analyzed. Results Serum UA level in ON group was significantly lower than that in control group (t=3.16,P＜0.05). However, no significant differences were found between ON and MS, ON and NMO, MS and NMO group (t=0.26, 0.94, 1.36;P＞0.05). Serum UA level was significantly lower in female than in male in all groups (F=6.27, 16.20, 21.09, 11.96;P＜0.05). In male and female patients of ON group, UA levels were significantly lower when compared with same gender in control group(t=2.13, 3.04;P＜0.05). However, no differences (P＞0.05) were found between ON and MS of same gender (t=0.25, 0.59), ON and NMO of same gender (t=0.33, 0.63), MS and NMO of same gender (t=0.63, 1.41). Patients with recurrent ON had lower serum UA level than that with first episodes (F=2.73). Patients with duration of over a year had lower serum UA level than that with duration of less than a year (F=0.23). Patients with retrobulbar neuritis also had lower serum UA level than that with papillitis (F=0.76). But the differences were not significant (P＞0.05). Conclusions A reduced serum UA level is found in patients with ON compared with healthy control. But serum UA level is not correlated with recurrence, lesion site or duration of disease.