Powdery mildew disease caused by the fungus Erysiphe polygoni D.C. is an important disease of mungbean. Loss can be more serious if the disease attacks at seedling stage. In this paper, we report genetics of the resistance to powdery mildew disease in mungbean using a recombinant inbred line (RIL) population derived from a cross between the susceptible parent "KPS1" and the resistant parent "VC6468-11-1A". Five hundred and ninety-two RILs were developed by random descending from $200;F_2$ plants. The population was evaluated against the fungus in field and greenhouse conditions. The data were analyzed following a nested design for self-pollinating plants to determine genetic heritability of powdery mildew resistance. The severity of the infestation was measured by using disease index (DI) and area under disease progress curve (AUDPC). Both values showed continuous distribution in the RILs. Under field conditions, the narrow-sense heritability of Dr and AUDPC were 0.67 and 0.48, respectively. While under greenhouse conditions, the values were 0.68 and 0.62, respectively. The results suggested that the resistance is quantitatively inherited with high heritability and predominantly additive gene action. To develop powdery mildew-resistant mungbean varieties, the plant breeder can select for resistant lines by using standard selection procedures for self-pollinating crops, viz. pedigree selection, bulk selection, early generation testing, and single-seed descent.