Streptococcal myositis is an extremely uncommon infectious disease that is caused by Group A Streptococcus (GAS). A GAS infection spreads rapidly and diffusely through the muscle, resulting in edema and necrosis. This can lead to streptococcal toxic shock syndrome with an extremely hig mortality. We report a 42 year-old female patient with Streptococcal myositis accompanying with systemic lupus erythematosus who initially presented with fever, severe pain, and tenderness on the calf without any prodromal symptom of myositis. Despite the aggressive management, her general symptoms were aggravated and she died 7 days later as result of the toxic shock syndrome.