Mutant analysis is one of most optimized genome-wide approach towards acquiring utile phenotypes and defining related genes. Gamma-irradiation, an acknowledged way of mutant-generating method, was applied to gain sets of mutant line in Brachypodium distachyon. B. distachyon is a model plant, commonly used in genus of Gramineae for the research of structure genomics and functional genomics. B. distachyon contribute to rapid and easy analysis because of its small size and quick growth. Mutant population was generated by different doses of gamma-irradiation (0, 50, 100, 150, 200, 250 Gy) in the gamma field phytotron. Distance from the source gives same irradiation duration for each plant. Plant growth parameters such as plant height, tiller number, leaf length & width, internode number & diameter, maturity and yield components (ear number biomass) were scored on M0 plants. Plant responses to different doses of radiation are evaluated and the effective radiation dosages to generate mutant using gamma-phytotron are suggested. Chronic irradiation using gamma-phytotron is useful tool to generate mutants for genomic variations such as SNP or INDEL as well as suitable for functional study of genes in Gramineae.