A study was conducted to determine the effects of forage soybean cultivar on chemical composition, ensiling characteristics, and ruminal degradability of silage. Two cultivars of forage soybean (Kodiak and Mammouth) were field-grown, harvested at the R6 stage, and ensiled in mini-silos (n = 3) for 0, 2, 4, 8, 16 and 45 d. Two ruminally fistulated cows were used to determine in situ ruminal nutrient degradabilities of the 45-d silages. Both cultivars went through slow fermentation as indicated by a gradual decline in pH up to day 45 post-ensiling. Lactic acid concentration increased throughout ensiling and was higher for Mammouth than Kodiak except at day 45 post-ensiling. Analysis of the 45-d silages showed that Mammouth contained higher neutral detergent fiber (NDF, 490 vs. 444 g kg-1), acid detergent fiber (371 vs. 353 g kg-1) and acid detergent lignin (81 vs. 64 g kg-1) than Kodiak. However, crude protein (CP) concentration was higher for Kodiak than Mammouth. Mammouth silage had lower buffer soluble protein and higher neutral and acid detergent insoluble protein concentrations than Kodiak silage. Results of the in situ study indicated that Kodiak silage had greater ruminal dry matter (606 vs. 549 g kg-1), CP (828 vs. 752 g kg -1) and NDF (272 vs. 227 g kg-1) degradabilities than Mammouth. It was concluded that chemical composition and ruminal nutrient degradabilities of forage soybean silage were significantly influenced by cultivar. Key words: Soybean [Glycine max (L.) Merill.], silage, ensiling; forage quality, nutrient degradability