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Biodiversity is one of the prominent characteristics of Golestan National Park in north of Iran which made the park one of the biosphere reserves in all over the world. Occurrence of several fires (67 fires from 1957 to 1999) in this park can reduce the floristic richness and disturb the sustainability of the environment and lower its world wide importance. To investigate the consequence of fire and changes that usually take place in vegetation structure in ecological succession, the 720 ha Takhti Yeylagh area located in southern part of the park was selected. This area had fire in August 1995. In this study, canopy cover, phytomass and diversity were investigated and compared, for both fired and control areas. The analysis showed that canopy percentage and phytomass in the fired and control areas had significant differences and their amount increased significantly in the fired area, whereas the diversity of the two areas had no significant difference. Also, this research indicated significant increase in Gramineae likes Stipa pennata, Festuca valessiana, Avena wiestii and Aegilops tauschii in the fired area compared to surrounding control area, but woody species like Acanthophyllurn pugens , Rosa persica, Cotoneaster ovatus and Onobrychis cornuta had considerable decrease. Due to the increase in annual species (especially Gramineae) and decrease in woody species, it can be concluded that fire is a preventing parameter in dynamic evolution of ecosystem towards climax, and that the dominance of Gramineae can increase the chance fire in the future.