Water hyacinth biomass (WHB)was used as a substrate for lactic acid production in the present study. Lactic acid (LaA) is one of the top fifteen rostrum chemicals derived from lignocellulosic biomass. For the increase of the required product quality, pretreatment of the substrate (WHB) was needed. Among the pretreatment method, the Organosoly pretreatment process was used in this study due to its simplicity, low cost, ease of separation that reduces energy consumption, and less toxicity as compared to other chemical pretreatment processes. This pretreatment process was applied with EtOH/water in different mixing ratios. The raw and pretreated WHB were characterized for their composition using NREL and ASTM protocols. It is found that the raw WHB has a composition of 44.8% cellulose, 25.12% hemicellulose, and 6.58% lignin with a balance of extractive and ash. The EtOH/water pretreatment was performed by CCD for delignification and enhancing sugar content in order to upgrade the quality of lactic acid and simplify the hydrolysis step. The hydrolysis process was done by using the heterogeneous catalyst for strengthening of environmental regulation, enhancing an adsorption and an isomerization of reduced sugar on the catalyst surface. It is an attractiveness strategy for the replacement of corrosive and harmful traditional mineral acid catalyst due to the presence of oxygenated and carboxylic groups together with Lewis acid site caused by the electron inductive effect of sulfonic groups In this study, the effect of pretreatment conditions on the hemicellulose recovery and delignification was investigated in order to optimize the hydrolysis process conditions for lactic acid production. The optimization was done by using BBD taking account of temperature, time, and catalyst concentration. It is found that temperature of 140 ℃, contact time of 90 min, and EtOH/Water ratios of 12.5L/g were the optimal conditions for the pretreatment process. At this optimal condition, 60.07% of lignin removal, 84.2% of holocellulose recovery, and the reduced sugar (32.13g/L or 64.26%) was measured by the DNS method. The recovered hollocellulose was hydrolyzed by the solid-acid Graphene oxide catalyst synthesized from pure graphite powder through the improved hammers method and characterized by FTIR and XRD. Lastly, 0.3432g of lactic acid per gram of biomass or 34.2% yield at 45 minute) was quantified by different analytical methods like LA standard method and FTIR spectrum. Keywords:- Water Hyacinth, Organosoly Pretreatment, Acid Hydrolysis, graphene oxide catalyst, Lactic Acid.