Abstract： Objective To observe and evaluate clinical effect of palonosetron hydrochloride and ondansetron hydrochloride that are used to prevent the chemotherapy-induced nausea and vomiting(CINV)caused by moderately emetogenic chemotherapy.Methods Sixty cases of cancer chemotherapy were divided into 2 groups:palonosetron group(n =30)and ondansetron group(n =30).Palonosetron group were given palonosetron hydrochloride 0.25 mg,intravenous infusion 30 min before chemotherapy on the first day.Ondansetron group was given ondansetron hydrochloride 8 mg,slow intravenous infusion 30 min before chemotherapy for three days.Dexamethasone 5 mg intravenous injection was used in the two groups.The situation of nausea and vomiting and adverse reactions were observed and recorded respectively in a period of 5 days after chemotherapy.Results In controlling acute CINV,the complete remission rate in palonosetron group was 80.0％ (24/30)and it was 76.7％ (23/30)in ondansetron group (P ＞ 0.05).The effective rate in palonosetron group was 93.3％ (28/30)and it was 86.7％ in ondansetron group (26/30)(P ＞ 0.05).In controlling delayed CINV,palonosetron hydrochloride was superior to ondansetron hydrochloride.The complete remission rate in palonosetron group was 76.7％ (23/30)and it was 63.3％ (19/30)in ondansetron group (P＞0.05).The effective rate was 93.4％ (28/30)in palonosetron group and 73.3％ (22/ 30)in ondansetron group(P ＜ 0.05).There was no significant difference in the adverse reactions between the two groups (P ＞ 0.05).Conclusions Palonosetron hydrochloride is superior to ondansetron hydrochloride in controlling delayed CINV caused by moderately emetogenic chemotherapy.There is no significant difference in controlling delayed CINV.It has few adverse reactions and should be used widely in clinic.