We present a 29-year-old woman with pT2N0M0 breast cancer, histological diagnosis of invasive ductal carcinoma, ER and PR low positive, and HER-2 (3+). The patient developed trastuzumab-induced thrombocytopenia in 6 hours after an intravenous infusion of trastuzumab at the second cycle of trastuzumab treatment with the symptom of abnormal uterine bleeding. Laboratory exam revealed a sharp drop of platelet count down to 3×109/L. With the treatment of single-donor platelet transfusions, glucocorticoids, oxytocin and thrombopoietic drugs, the platelet count recovered completely in 11 days. This case was confirmed to be severe thrombocytopenia induced by trastuzumab, and retreatment with trastuzumab was not attempted. With increasing clinical utilization of trastuzumab, clinicians are likely to encounter more life-threatening trastuzumab induced severe thrombocytopenia. By this case report and literature review, we hope to increase the awareness, attach the attentions to this condition, and help with the effective treatment.