Immunoglobulin A vasculitis (IgAV) is a systemic small-vessel vasculitis caused by the deposition of IgA-based immune complexes, with myalgia being a rare complication. This study reports a pediatric case of IgAV with fasciitis. A five-year-old boy with no previous medical history was admitted to the hospital with abdominal pain and repeated bilious vomiting. Palpable purpura was observed on his face and right upper limb. Abdominal ultrasound and contrast-enhanced CT revealed decreased peristalsis and wall thickening of the fluid-filled duodenum, leading to a diagnosis of IgAV. Initial treatment with prednisolone and fasting improved his symptoms, but he complained of bilateral calf pain from day five with normal creatinine kinase levels. Fat-suppressed MRI on day 10 revealed high-signal areas around the soleus muscle, diagnosing fasciitis. Following steroid dose reduction, his myalgia worsened with difficulty falling asleep and the disability of standing up. Increasing the prednisolone dose alleviated his symptoms. The patient was discharged on day 23 without further myalgia. The pathogenesis of myalgia in IgAV remains unclear, but this case indicated a complication of fascial vasculitis and the effectiveness of steroid therapy. In conclusion, IgAV can be complicated by muscle involvement, and fasciitis should be considered a differential diagnosis of myalgia when creatinine kinase levels are normal. While supportive care is primary, steroid therapy should be considered depending on disease severity.