In this study, a fungal strain was isolated from soil contaminated with fruit wastes and screened for citric acid production and it was identified as Aspergillus niger. The solid wastesubstrates like fruit peels (grapes, mosambi peel) and bagasse with varying particle sizes of M1 (0. 250mm), M2 (0.150mm) and M3 (0.63mm) and 4% methanol, 70% moisture level was maintained throughout the solid state fermentation process for the citric acid production from the fungal culture. The Aspergillus niger produces the higher yields of citric acid where grape peel with particle size 0.63mm as a substrate in the medium. Higher fungal biomass and protein contents estimated in grapes (M3), mosambi (M1) and bagasse (M3) wastes substrates respectively in the solid state fermentation.