Inflammatory myositis as an extra-intestinal manifestation of inflammatory bowel disease (IBD) is rare. Coexistence of immuno-mediated diseases in patients with IBD and myositis suggests a common etiopathogenic mechanism underlying these conditions. The current report refers to a rare case of a 45-year-old Korean female with ulcerative colitis (UC) who developed dermatomyositis. She presented with skin rash and proximal muscle weakness, and her disease activity of UC was in remission state. Electromyography, magnetic resonance imaging, and deltoid muscle biopsy were performed. She was diagnosed with dermatomyositis associated with UC and treatment with glucocorticoids and azathioprine resulted in improvement in muscle power and skin rash. Clinicians should be aware of this unusual extra-intestinal manifestation.