Lignocellulosic biomass, Water hyacinth (Eichornia crassipes) was pretreated with ionic-liquid (IL)-water mixture using ILs, 1-butyl-3-methylimidazolium acetate [BMIM]OAc, 1-butyl-3-methylimidazolium chloride [BMIM]Cl, 1-butyl-3-methylimidazolium bromide [BMIM]Br and 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM]TFB. Effects of IL anions, IL content, temperature, time and particle size of biomass on dissolution and recovery of lignin were examined and the conditions were optimized. Biomass dissolution and yield of lignin recovery in ILwater mixtures with different anions of 1-butyl-3-methyl imidazolium based ILs follows the order, [BMIM]OAc>[BMIM]Cl>[BMIM]Br>[BMIM]TFB. The role of IL-water mixture for dissolution and recovery of lignin was investigated by characterizations using XRD, SEM, FTIR, TGA and XRF spectroscopy. The Hildebrand solubility parameters of biomass component (lignin) and IL-water mixtures were examined using intrinsic viscosity method. On applying the concept of Hildebrand solubility parameter for dissolution of the biomass in all the IL-water mixtures the results were consistent with the experimental results, which suggests that Hildebrand solubility parameter concept can be applied as primary information in choosing the appropriate solvent for biomass dissolution.