Ionic liquid (IL) pretreatment of lignocellulose materials is a promising process in biomass conversion to renewable biofuel. More in-depth research involving environment-friendly IL is much needed to explore pretreatment green route. In our case, IL 1-methyl-3-methylimidazolium dimethylphosphite ([Mmim]DMP) was chosen as an environment-friendly solvent to pretreat corn cob in view of its biocompatibility with both lignocellulose solubility and cellulase activity. The pretreatment/saccharification process and in situ saccharification process involving [Mmim]DMP were efficiently performed in bioconversion of corn cob to sugars, and more than 70% saccharification rates were obtained. Furthermore, the fermentability of reducing sugars obtained from the hydrolyzates was evaluated using Rhodococcus opacus strain ACCC41043 (R. opacus). High lipid production 41-43% of cell dry matter was obtained after 30 h of cultivation. GC/MS analysis indicated that lipids from R. opacus contained mainly long-chain fatty acids with four major constituent/oleic acid, stearic acid, palmitic acid, palmitoleic acid which are good candidates for biodiesel. These elucidated that corn cob pretreated by IL [Mmim]DMP did not bring negative effects on saccharification, cell growth, and accumulation of lipid of R. opacus. In conclusion, the IL [Mmim]DMP shows promise as green pretreatment solvent for cellulosic materials.