The key requirement for an economical lignocellulosic ethanol production is efficient pretreatment, pretreatment includes physical, chemical, biological and thermal methods and their combinations. Even though there are various pretreatment methods Alkali and acid pretreatment methods are selected to comparatively study the compositions of the biomass in terms lignin, hemicellulose and cellulose at relatively mild operating condition. The rice straw collected from Wereta was prepared to have 0.5-0.59 mm particle size and pretreated with NaOH and H2SO4 at concentration range of 0.5-4.5 and contact time of 10-50 min for both of pretreatment methods. Compositional characterization was performed by NREL and ASTM protocols and the total reducing sugar concentrations after hydrolysis were determined by DNSA method. It is found that, the raw rice straw has a composition of 40.5 % cellulose, 25.6 % hemicelluloses, and 11% Lignin. The alkali pretreatment resulted in a maximum lignin removal of 88% at temperature of 60 oC, contact time of 50 min, and alkali concentration of 4.5%NaOH w/v, which leads to an increment of cellulose fraction to 82% and reduction of hemicellulose to 79.3 %. In the case of acid pretreatment maximum lignin and hemicellulose removal of 59.7% and 83.4% was recorded respectively at temperature of 121oC, contact time of 50 min, and concentration of 4.5% H2SO4 v/v, this leads to an increment of cellulose fraction to 78.3%. A maximum total reducing sugar yield of 165.6 mg/g and 108 mg/g were obtained for alkaline pretreated and dilute acid pretreated, respectively. Within the ranges of pretreatment conditions considered, increasing temperature, reaction time, and alkaline concentration favor the percent lignin removal and this increases total reducing sugar yields for alkaline pretreatment. For the hydrolysis experiments, as the acid concentration increases from 0.5 to 2.5 the fermentable sugar increases but decrease when the acid concentration increased from 2.5 to 4.5. This could be due to the formation of hydroxymethyl furfural (HMD) when the acid concentration exceeds the optimal values. Therefore, it is determined that alkaline pretreatment via dilute sulfuric acid hydrolysis is a better option for production of fermentable sugar from rice straw at relatively mild