This paper describles the experimental results of heat transfer performance of dropwise condensation in the two-phase closed thermosiphons. The results show that the heat transfer coefficient for dropwise condensation in the thermosiphon increases with an increase in the vapor temperature and decreases with increasing heat flux. The fact that the life tests have been conducted for 11340 hrs with oleic acid as the promoter indicates that dropwise condensation in the thermosiphon is hopeful for longlived operation. The heat transfer correlations of dropwise condensation in the water thermosiphons are obtained by the stepwise regression when oleic acid and silicon oil are used as the promoters.