Macrolides have both immunomodulatory and antibacterial effects. We report 3 cases of primary immune thrombocytopenia (ITP) patients who were successfully treated with macrolides, irrespective of Helicobacter pylori (H. pylori) infection status. Case 1, an 88-year-old woman who was an H. pylori-positive ITP patient, was treated with clarithromycin (CAM). CAM was effective temporarily. As an alternative to CAM, she was successfully treated with erythromycin (EM) for more than 7 months. Case 2, a 61-year-old man who was an H. pylori-negative ITP patient, was unsuccessfully treated with CAM but successfully treated with EM. Case 3, a 75-year-old woman who was a H. pylori-negative ITP patient, was treated with CAM. CAM was effective temporarily. After approximately 6 months, she was treated with EM for a common cold, and her platelet count increased rapidly. Based on these findings, macrolide treatment was effective for ITP. The effectiveness of macrolides might suggest immunomodulatory effects as well as antibacterial effects for H. pylori.