Abstract: Objective　To investigate clinical features, diagnosis and treatment in patient with activated phosphoinositide 3-kinase δ syndrome (APDS) caused by PIK3CD gene mutation. Methods　Data of one patient diagnosed as APDS combined with arthritis were retrospectively analyzed, and the related literatures were reviewed. Result　The patient was a 4 years and 10 months old boy with hepatosplenomegaly, lymph node enlargement, coughing accompanied by fever, and a history of recurrent respiratory infection. Serum IgG < 0.07 g/L, IgA < 0.07 G /L, IgM 1.78 g/L; The number of CD19+B cells and CD4+T cells decreased and the CD4+/CD8+ ratio was inverted, which suggested primary immunodeficiency disease. Gene test identified a heterozygous missense mutation c.G3061(p.E1021K) in PIK3CD gene , which confirmed the diagnosis of APDS. During hospitalization, swelling was observed on both knee joints, especially on the left side, and he was unable to walk. However, through intravenous injection of immunoglobulin and oral naproxen, swelling joints were obviously relieved, and he could walk independently. Conclusions　APDS is mainly manifested by recurrent respiratory tract infection, hepatosplenomegaly, enlargement of lymph node, high susceptibility to Epstein-Barr virus and cytomegalovirus. Some children may develop arthritis.