We investigated the seasonal variation of osmolytes accumulation in the leaves of 5 mangrove species : Kandelia obovata, Bruguiera gymnorrhiza, Rhizophora stylosa, Avicennia marina, Lumnitzera racemose planted in Uruma City of Okinawa Prefecture, and interspecific differences and factors affecting the seasonal variation of the osmolyte accumulation were discussed. Cation contents were different between species and between salt tolerance mechanisms. Salt content in the open ocean and leaf cation content showed no apparent difference among the sampling month. Leaf Na+ : K+ ratio showed little seasonal variation. Total soluble sugar content and total polyol content varied among month. Total soluble sugar content of all 5 species was high in winter and the effects of average temperature on total soluble sugar content was recognized. The seasonal variation of total polyol was different among tree species and factors affecting osmolyte accumulation varied among species. Seasonal variation of the osmolyte contents are related with environmental factors including monthly mean temperature, but not related with leaf cation contents.