Objective To explore the clinical features and treatment of activated PI 3 K 未 syndrome. Methods Clinical manifestations, laboratory examination and genetic testing and treatment in a child with activated PI3K 未 syndrome 1 (APDS) were retrospectively analyzed. Results The main clinical manifestations of this APDS 1 patient were recurrent respiratory tract, splenomegaly, lymph node enlargement, enteropathy, hyper IgM syndrome, decreased proportion of T lymphocytes and CD 4 + T lymphocytes. This patient was diagnosed as activated PI 3 K 未 syndrome 1 by whole exon sequencing, and was treated with antibiotics and gamma globulin, then the clinical symptoms were significantly improved. Conclusions For patients presenting with recurrent respiratory tract infections, lymphoproliferative diseases, bowel diseases, and hyper IgM syndrome, the possibility of activated PI 3 K 未 syndrome should be considered, and genetic testing should be performed when necessary to confirm the diagnosis. Combination of antibiotics and gamma globulin replacement therapy could achieve a good clinical outcome.