【Abstract】 Objective To investigate the efficacy and safety of olanzapine in the treatment of highly and moderately emetogenic chemotherapy induced nausea and vomiting (CINV). Methods 101 chemotherapy patients were randomly divided the test group (51 cases) and control group(50 cases). Before chemotherapy, the test group and the control group were intravenously given navoban tropisetron 5 mg and dexamethasone 5 mg. The test group was given olanzapine 5 mg daily started on the day of chemotherapy. The nausea and vomiting after chemotherapy were observee.Results The effective rate for prevention of acute CINV and delayed CINV for two groups were 803% and 863% in test group, respectively. The KPS score in test group was higher in control group. There was no statistical difference between the two groups in the incidence of dizziness, fatigue, constipation. However, the test group showed more good result in loss of appetite than control. Conclusion Small dose of olanzapine (5mg /d) for prevention of nausea and vomiting after chemotherapy is effective and safe.