Osteomalacia is characterized by defective mineralization of bone tissue, which leads to an accumulation of unmineralized bone matrix. The various potential causes of osteomalacia include vitamin D-associated metabolic disorders, absorption disorders, cancer, and drugs. While reports of osteomalacia caused by nutritional deficiency and inadequate sunlight exposure are rare in Korea, we recently experienced a case of osteomalacia due to vitamin D deficiency in a 36-year-old woman. The patient was a strict vegetarian, and over the previous 3 years, she had worked solely at night and reported suffering from multiple bone pain for 6 months. Dual-energy X-ray absorptiometry revealed a T-score of -4.9 and Z-score of -4.5 at the lumbar portion of the spine (L1-4). The serum 25(OH)D level was 7.6 ng/mL, and an iliac bone biopsy showed increased osteoid thickness compatible with osteomalacia. The patient’s symptoms of generalized bone pain improved after vitamin D and calcium supplementation.