The efficiency of quebracho (Schinopsis spp), acacia (Acacia spp) and chestnut (Castanea spp.) tannins to protect protein of soybean meal from in vitro degradation was determined. Each tannin was added to soybean meal at levels of 0, 2, 4, and 8% of dry weight and incubated by triplicate in ruminal liquor and McDougall buffer for 48 h (degradation by rumen bacteria) or 48 h plus 24 h of pepsin digestion (degradation by rumen bacteria plus pepsin). In vitro ammonia, isobutyric and isovaleric acid production decreased by addition of tannins to soybean meal. Reduction of ammonia and isobutyric acid per unit of tannin added (slope) was higher (P