Abstract: This study was carried out to determine the chemical composition and ruminal degradability of Soybean Straw (SBS). Samples were collected from several soybean grain threshing farms in Moghan, Iran. Chemical composition for Dry Matter (DM), Crude Protein (CP), Ether Extract (EE), Organic Matter (OM), Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF) and Acid Detergent Lignin (ADL) of pooled samples were 89.18, 5.10, 2.85, 96.90, 80.80, 63.20 and 13.00%, respectively. Degradation procedure was performed using nylon bags filled with 5 g of SBS and suspended in the rumen of three fistulated Gezel rams for 0, 2, 4, 8, 16, 24, 48 and 72 h and obtained data were fitted to a non-linear degradation model to calculate ruminal degradation characteristics. Results showed that soluble fraction (a) of SBS were very low, especially in case of DM and OM. Potential degradability (a + b) of SBS for DM, OM and CP were 36.97, 37.74 and 68.07% and for effective degradability (Out flow rate 0.02 h-1) were 21.40, 22.27 and 48.30%, respectively. It is conclude that, SBS have low DM and OM degradability and higher CP degradability in the rumen. Based on chemical composition and degradation characteristics, untreated SBS can be used in the ration of ruminant in limited levels.