Abstract: Objective To explore effective methods for estimating the size of male clients of street-based female sex workers(FSW).Methods Contacting subjects directly on the working sites of street-based FSW or with the help of street-based FSW volunteers who identified male clients at first,and applied indirect division methods to estimate the size of male clients of street-based FSW.Results There were 8 sites where street-based FSW frequently assembled together in the downtown district of the city,the size of male clients who made sex trade with street-based FSW in latest one year was 3 724~4 337,which was 1.69%~1.96% of the local grown male population,and the sex trade frequency of these male clients was 16.0 times per year.Conclusion Applying indirect division methods could estimate the size of male clients who made sex trade with street-based FSW simply and quickly.