A 73-year-old male patient with postoperative recurrent rectal cancer developed thrombocytopenia after XELOX therapy. Thrombocytopenia persisted despite chemotherapy discontinuation;therefore, he was referred to our department for further evaluation. Bone marrow specimen examination revealed increased immature megakaryocytes and blood test results revealed elevated platelet-associated immunoglobulin G (PA-IgG) levels, leading to immune thrombocytopenic purpura diagnosis. His platelet count recovered after prednisolone therapy. Eltrombopag treatment was introduced considering thrombocytopenia secondary to chemotherapy resumption for rectal cancer. FOLFIRI therapy was continued without platelet count reduction, and PA-IgG levels decreased over time. The patient continued chemotherapy with eltrombopag and achieved a complete treatment response.