Granulocyte colony stimulating factor (G-CSF) has been widely used as a mobilizing agent to rapidly increase peripheral blood stem and progenitor cells. Limited data is available for G-CSF-associated late-onset coronary thrombosis and thrombocytosis. We report a case of a 23-year-old Chinese Han patient who presented with acute myocardial infarction and thrombocytosis after finishing bone marrow harvesting and peripheral blood stem cell collection following G-CSF treatment several days later. By using antiplatelet drugs and undergoing percutaneous transluminal coronary angioplasty, the patient’s symptoms were relieved and his platelet level decreased to normal. This is the first suspected case report of late-onset coronary thrombosis and thrombocytosis related to G-CSF. Caution should be taken for the delayed adverse reactions in patients undergoing G-CSF mobilizing.