Sweet sorghum is a bioenergy crop and is a good source for biogas and bioethanol production. Sweet sorghum stalk contains free sugars,cellulose, and hemicellulose.The stalk is rich in soluble sugars, i.e., sucrose, glucose, and fructose as well as insoluble carbohydrates, i.e., cellulose and hemicelluloses, which all can be utilized as raw materials for ethanol and biogas production.It is difficult to improve the overall yield of ethanol and biogas from sweet sorghum by most of pretreatment, as the stalks contain free sugar that which are wasted in most of the common pretreatments. In this study, effect of organosolv pretreatment to improve biogas and ethanol was investigated.In the first step effect of temperature (100,120,140,160 o C), ethanol concentration, and presence of sulfuric acid (as catalyst) was studied on improvement of biogas production from the solid residue of the stalk after the pretreatment.The organosolv pretreatment process was conducted using a high-pressure stainless steel vessel (as a batch reactor) with a working volume of 500mL. The reactor was equipped with a pressure gage and a thermometer, and it was placed in an oil bath equipped with a temperature controller.Liquid fraction was distillated to recover the ethanol. The untreated and organosolv-treatment samples were digested in 118 mL batch digesters.Biogas experiments were carried out at mesophilic conditions (37 °C). Gas samples were analyzed for methane and carbon dioxide concentrations using gas chromatography(GC). Biogas production by increasing pretreatment temperature was improved. The sample treated at 160 o C, 50% ethanol, without catalyst resulted in the maximum yield among solid substrates (untreated and pretreated). In the second step mixture of liquid fraction and solid residue was used for biogas production. The maximum amount of biogas production was related to mixture of liquid and solid fraction treated at 160 o C without catalyst using 50% ethanol concentration (278 ml CH4/g VS(.This wasmore than 270% higher than the yield of biogas from untreated sweet sorghum stalk. At the third step enzymatic hydrolysis of the untreated and all treated sweet sorghum were conducted at 45 °C for 96 h with enzyme loading of 20 FPU cellulase and 50 IU ?-glucosidase per gram of substrate. The best pretreatment conditions were 50% ethanol, 1% sulfuric acid, and 140 o C. This pretreatment improved the glucose yield from 34.1% theoretical yield for the untreated sweet sorghum to 83% for the pretreated sample.. Consequently, ethanol production yield from pretreated materials was2-fold higher than that of untreated wood. The liquid fraction of pretreatment after distillation (liquor) was used directly for ethanol production. The maximum ethanol yield (59.4% of theoretical yield) was obtained from liquor produced at 100?C, without catalyst, 50% ethanol-water solution. The analysis showed that organosolv pretreatment at elevated temperature can significantly reduce the lignin and xylan contents and the cellulose crystallinity which is more amenable for anaerobic digestion and enzymatic hydrolysis. On the other hand, liquid fraction of pretreated materialhad a good potential for ethanolic fermentation and also biogas production (in mixture with the solid residue). Key words organosolv pretreatment, sweet sorghum, biogas, ethanol, sulfuric acid, anaerobic digestion, enzymatic hydrolysi