Abstract: The aim of this study was to determine the effect of ensiling of alfalfa plant with sorghum plant on the chemical composition and nutritive value of silage mixtures using in vitro gas production technique. Chemical composition including; Dry Matter (DM), Crude Protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Ash Volatile Fatty Acids (VFA), lactic acid and pH were determind. Gas productions were determined at 0, 3, 6, 12, 24, 48, 72 and 96 h incubation times and their kinetics were estimated using the exponential equation Y = A (1 - exp•^ct). The Organic Matter Digestibility (OMD) and Metabolisable Energy (ME) of the resultant silages were estimated. Ensiling of alfalfa plant with sorghum plant had a significant effect on the chemical composition, fermentation parameters, potential gas production, OMD and ME values of the resultant silages. Ensiling of alfalfa with sorghum plant increased the lactate and propionate production, OMD, ME but decreased acetate and butyrate production, CP content and pH of the resultant silage. As a conclusion, ensiling of alfalfa plant with sorghum plant will overcome some of the drawbacks related to low DM and water soluble carbohydrate contents and high buffering capacity of alfalfa plant.