Inclusion body myositis has been recognized as a major form of idiopathic inflammatory myopathy. An old male patient with insidious onset and slowly progressive muscular weakness and artrophy has been reported in this article. The duration of symptom before biopsy was 23 years. The first symptom was dysphagia, and muscular weakness developed seven years later. Muscular atrophy was predominant symmetrically and proximally, particularly the quadriceps femoris muscles. Cervical and abdominal muscles were also affected. Myalgia was absent. Electromyogrophy showed myopathic alterations. Erythrocyte sedimentation rate, creatine kinase, immunoglobulins G increased slightly or moderately. Rheumatoid factor was positive, and he had been diagnosed as having rheumatoid arthritis for 23 years. Inclusion body myositis was ultimately diagnosed based on the muscle biopsy which showed mononuclear cell invasion of nonnecrotic muscle fibers, the characteristic rimmed vacuoles in cryostat sections and cytoplasmic inclusion bodies consisted of plenty of tubulofilaments by electron microscope.