Alkaline pretreatment has been known as the most popular method to process lignocellulosic materials for bioethanol production due to its simplicity and high efficiency. However, the waste water from the alkaline pretreatment has a very high basicity, which requires neutralization with acids upon further disposal. In this study, Field pea straw was employed as lignocellulosic material and its pretreatment was inspected with diluted NaOH and H2SO4 in different combination ways. The raw and pretreated field pea straws were characterized for their composition using National Renewable Energy Laboratory (NREL) and American Standard for Testing Materials (ASTM) protocols. It is found that, the raw field pea straw has a composition of 44.9 % cellulose, 20.4 % hemicelluloses, and 13.7% Lignin. Dilute NaOH pretreatment was performed in the first stage primarily for delignification while, the second stage was carried out by using dilute H2SO4 mainly for hemicellulose solubilization. Hereby, acid was used not only for hemicellulose solubilization and waste water neutralization but also to contribute to lignin removal. Finally, alkaline waste water can be mixed to be neutralized with acidic waste from the acidic hydrolysis. During the process, the pretreated liquid collected from the second stage and liquid hydrolysates after acidic hydrolysis of the solid recovered from the second stage were stored for reducing sugar measurement using Dinitrosalicyclic acid (DNSA) method. Solid residues from both stages were subjected for the analysis lignin removal and cellulose recovery. The process was optimized by using central composite design (CCD) analysis taking account of temperature, residence time, alkali and acid concentration. The optimal condition 135°C, 48 min, 1.89 % (w/v) NaOH, and 1.61% (w/w) H2SO4 was obtained. The two-stage pretreatments under these optimal conditions gave 0.425 g/g reducing sugar and 88.92% lignin removal and the alkaline pretreatment under the same conditions gave 0.393 g/g reducing sugar and 83.2% lignin removal where as the acidic pretreatment gave 0.338 g/g reducing sugar and 48.5% lignin removal. Hence, the designed two-stage pretreatment process has large potential to achieve the commercial conversion of lignocellulosic biomass into fermentable sugars.