The rice brown spot disease caused by Bipolaris spp., is one of the most important diseases in Iran and world. In this research, 135 fungal isolates were isolated from 256 collected samples in Guilan province fields. The base of identification was morphological characteristics of fungi. According to the results, the fungal isolates belonged to: Bipolaris oryzae, Bipolaris victoriae, Alternaria tenuissima, Alternaria infectoria, Alternaria citri, Alternaria alternata, Alternaria franseriae and Alternaria pellucida. The pathogenicity test revealed that all isolates of B. victoriae were pathogenic. In laboratory, we used various methods such as dual culture, inhibition of B. victoriae growth by culture filtrate, dual culture of the studied antagonistic fungi and B. victoriae by slide culture method and effect of volatile metabolites on inhibition of growth of this fungus. Based on results, A. pellucida, A. alternata, A. franseriae, A. tenuissima, A. infectoria and A. citri had the highest percentage of mycelial growth inhibition of B. victoriae, respectively. In greenhouse studies, these fungi were inoculated on rice. All of the isolates, except A. tenuissima effectively reduced disease rating of B. victoriae, and A. pellucida with 38.76% reduction in disease rating was the most effective antagonist in greenhouse studies. The results showed that there are avirulent isolates of Alternaria spp. that can be introduced as potential antagonists to control brown spot disease of rice.