Above ground tree biomass was estimated in Bruguiera parviflora, B. sexangula, and Rhizophora apiculata communities of a mangrove forest in Talidendang Besar, East Sumatra, Indonesia. The research was carried out from December 1990 to January 1991, and allometric relation method was used to estimate the above ground biomass of tree species having a diameter of 10 cm and over. The above ground biomass in this forest ranged from 42.94 to 89.68 t d.wt/ha in a B. parviflora community; 75.99 to 279.03 t d.wt/ha in a B. sexangula community; and 40.70 t d.wt/ha in a R. apiculata community.