An investigation was carried out at All India Coordinated Sorghum Improvement Project, Main Agricultural Research Station, Dharwad during kharif 2012. Different doses of gamma rays (300 Gy, 350 Gy and 400 Gy) were used to irradiate seeds of two sorghum varieties viz., DSV-6 and CSV-15 in order to study genetic variability for grain size and productivity related traits in M₂ progenies of kharif sorghum. The results indicated relatively wider range of performance of M₂ progenies of 400 Gy dose for most of the characters studied including grain size in both genotypes. The mean and range values of the M₂ progenies of both genotypes amply indicated possibility of enhancement of seed size and grain yield per plant. The GCV and PCV estimates showed wide variation for most of the characters in segregating M₂ progenies. High GCV and PCV estimates were exhibited for grain yield per plant in all M₂ progenies of DSV-6 and CSV-15 genotypes. Most of the characters under study exhibited moderate to high heritability in all the six M₂ progenies of two genotypes. High heritability values of more than 90 per cent have been observed for plant height across six M₂ progenies. High heritability coupled with high genetic advance as per cent over mean was observed for grain yield per plant under all irradiated M₂ progenies of DSV-6 and CSV-15 genotypes.