Abstract: Guanine nucleotide exchange factor, an important G protein regulator, activates the G protein regulated signal pathways by switching on G protein from GDP-bound to GTP-bound state. Based on the genome annotation, the gene locus Mgg_11178.6 encodes a guanine nucleotide exchange factor for Rho GTPases (designated as MoRGF1) in Magnaporthe oryzae. Phylogenetic analysis showed that MoRGF1 shared high identiy with its homologs from other filamentous fungi. Two MoRGF1 deletion mutants, obtained by homologous recombination, displayed slower growth and obviously reduced conidiation, although with no change in pathogenicity when compared with their wild type. Our results suggested the putative RhoGEF may involve in regulation of growth and conidiation in M. oryzae.