Abstract: Objective To conducta phaseⅠclinical trial for pandemic influenza split-virion vaccine H5N1 and to assess the safety of the vaccine.Methods We conducted a single center,stratified-random,double-blind,placebo-con trolled trial involving healthy adults aged 16 to 60 years who were assigned in a 1:1:1:1 ratio to receive two doses schedule(admin is tered on days 0 and 21)of placebo(n=33)or an inactivated split-virion influenza A(H5N1)vaccine with 7.50μg(n=33),15.0μg(n=33),30.0μg(n=33).Results In the stage of clinical trial and follow-up,no abnormal reaction,coupling reaction and any clinical significant serious adverse event was reported.Most of the reactions in all vaccine formulations wereⅠgrade local reactions recovered with in 48 hours.Reactions in treatment group were significantly higher than that of in placebo control group(χ²=25.2825,P<0.0001).The local and the systemic reaction rate of the group with 30.0 μg dose was the highest(78.79% and 51.52%).Reaction rate was 100% higher for the first dose than that of the second.Conclusion Pandemic influenza split-virion vaccine had better security,no gradeⅢ and above of adverse reaction occured.