An efficient conversion of lignocellulose into fermentable sugars is a key step in producing bioethanol in a cost effective and eco-friendly manner. Alternative source like water hyacinth biomass (WHB) (Eichhornia crassipes) as lignocellulosic material may be used as a feedstock for production of fermentable sugars. Mainly the cellulose, hemicellulose, lignin, ash and extractive components of water hyacinth biomass was determined and found to be 37.28%, 30.21%, 14.31%, 8.1% and 10.1% respectively. Then the effects of alkali (NaOH) concentration (2.5, 4.5 and 6.5%), treatment time (70 min, 100 min and 130 min) and temperature (60 °C, 90 °C and 120 °C) on lignin removal, cellulose recovery and reducing sugar yield were investigated by employing full factorial design. Results indicated that they all conditions influenced the efficiency of water hyacinth biomass pretreatment. Maximum lignin removal, hemicellulose recovery and maximum reducing sugar of 72.53%, 71.48% and 343.265 mg/g was obtained respectively at a treatment conditions of 4.5% w/v alkali (NaOH) concentration, 100 minute treatment time and 90 °C operating temperature. Finally, hydrolysis of pretreated water hyacinth biomass was performed with 1.5% v/v dilute sulfuric acid for 120 minute at 121°C/15psi in an autoclave. The optimum reducing sugar obtained was 343.265 mg/g at a treatment condition of 4.5% alkali (NaOH) concentration, 100 minute treatment time and 90 °C treatment temperature. Generally, the combined cellulose and hemicellulose content of water hyacinth reaches 67.49% and the lignin content is found to be 14.31%, which is low. Therefore, water hyacinth biomass could be used as a feedstock for fermentable sugar production.