Zagros forests are mainly covered by Quercus brantii L.coppices and oak sprout clumps occupy the forest area like patches.We investigated post-fire herbaceous diversity in the first growing season after fire.For this purpose neighboring burned and unburned areas were selected with the same plant species and ecological conditions.The data were collected from areas subjected to different fire severities.Overall 6treatments were considered with respect to fire severity and the microsites of inside and outside of oak sprout clumps including:unburned inside and outside of sprout clumps(Ni and No),inside of sprout clumps that burned with high fire severity(H),inside of sprout clumps that burned with moderate fire severity(M),outside of sprout clumps that burned with low fire severity(OH and OM).Different herbaceous composition was observed in the unburned inside and outside of oak sprout clumps.The species diversity and richness were increased in treatments burned with low and moderate fire severity.However,in treatment burned with high fire severity(H),herbaceous cover was reduced,evenness was increased,and richness and diversity were not significantly changed.We concluded that besides the microsites conditions in forest,fire severity is an inseparable part of the ecological effect of fire on herbaceous composition. Zagros forests are mainly covered by Quercus brantii L.coppices and oak sprout clumps occupy the forest area like patches. We investigated post-fire herbaceous diversity in the first growing season after fire. For this purpose addressed burned and unburned areas were selected with the same plant species and ecological conditions. the data were collected from areas subjected to different fire severities. Overall 6treatments were considered with respect to fire severity and the microsites of inside and outside of oak sprout clumps including: unburned inside and outside of sprout clumps (Ni and Inside of sprout clumps that burned with high fire severity (H), inside of sprout clumps that burned with moderate fire severity (M), outside of sprout clumps that burned with low fire severity (OH and OM) .Different herbaceous composition was observed in the unburned inside and outside of oak sprout clumps.The species diversity and richness were increased in treatments burned with low and moderate fire severity. However, in treatment burned with high fire severity (H), herbaceous cover was reduced, evenness was increased, and richness and diversity were not significantly changed. We concluded that besides the microsites conditions in forest, fire severity is an inseparable part of the ecological effect of fire on herbaceous composition.