Serum 25(OH)D levels were reduced in anti-NMDAR encephalitis patients. 25(OH)D levels were lower in female subgroup than that in male subgroup. 25(OH)D levels were lower in severe impairment subgroup than that in mild symptoms subgroup. 25(OH)D levels were lower in those with limited treatment than those with favorable treatment. Serum 25(OH)D levels were significantly associated with age, disease severity.