52-year-old man, presented with chronic cough and dyspnea 1 year. April 2018, computed tomography of chest showed a 6x11 cm. well defined contour and lobular enhancing mass at right anterior mediastinal, suspected for thymoma. Biopsy was done, and reported thymoma type A. IHC positive for AE1/AE2, CD99, PAX8 and negative for CD12, TdT, CD34, S100, SMA, desmin, STAT6. He was planned for thymectomy, however, he was early hospitalized because developed Campylobacter jejuni pneumonia. Ceftriaxone with azithromycin were prescribed as the blood culture sensitivity report.C. jejuni usually was virulent in immunocompromised host. He was noted to have leukopenia and pneumonia was failure to improve. Investigations for leukopenia found hypogammaglobulinemia that IgA <0.05 mg/ml (0.7-4.0), IgG 0.57 mg/ml (7-16), IgM < 0.05 (0.4-2.3), low CD4 count 338 cells/uL (470-1404), CD8 500 cells/uL(360-1250), CD4/CD8 ratio 0.78 (0.65-2.49). The diagnosed was Good syndrome associated with thymoma. Treatment by intravenous immunoglobulin (IVIG) 0.45 g/kg for 1 dose and adjusted antibiotics to Piperacillin/tazobactam. 1 week later, CBC was normal level and pneumonia was resolved. June 2018, thymectomy was done; the pathological report was thymoma type AB, size 10.5*7.6 cm, no trans-capsular invasion and free margin. Postoperative, immunoglobulin level was still decrease IgA <0.04, IgG 3.51, IgM<0.01 mg/ml. thus IVIG were re-prescribed, and immunoglobulin levels were evaluating every month. Thymoma was planned to surveillance. Good syndrome (immunodeficiency with concomitant thymoma) is an adult-onset hypogammaglobulinemia that is the rare cause of combined B- and T-cell immunodeficiency, results in increase susceptibility to opportunistic infections. Pathogenesis of the disease remains unknown. The immunodeficiency may precede or follow the diagnosis of a thymoma, but the immunologic abnormalities cannot be corrected by thymectomy. IVIG should be given if humoral immunodeficiency is demonstrated. Immunophenotyping is essential in detecting and periodically monitoring. Recognition of hypogammaglobulinemia is an important clinical consideration, since the prognosis for patients with Good syndrome appears worse.