The effects of commercial chestnut (CWE) and quebracho (QUE) extract at different inclusion levels to soybean meal (SBM) on the in vitro degradability and digestibility of dry matter (DM) and crude protein (CP) were evaluated. Samples were prepared by mixing 0 (CON), 15, 30, and 60 g/kg of CWE and QUE with SBM, soaked in water overnight at room temperature, dried, and ground. Samples were incubated in duplicate in buffered rumen fluid for 24 hr at 39°C. In vitro rumen degradability of DM and CP of tannin‐treated SBM decreased with increasing quantities of tannins, especially with CWE‐treated SBM. In vitro abomasal (pepsin‐HCl) digestibility of the DM and CP was only slightly suppressed. As a result, rumen by‐pass protein (BP‐CP) increased with increased quantities of tannins, especially with CWE‐treated SBM. In comparison with nontreated SBM, the BP‐CP digestibility did not decrease, except with the highest quantity of QUE. Treatment of the SBM with tannins, especially with CWE, increased flow of the undegraded protein to the abomasum, suggesting the better supply of the ruminant animal with amino acids. In vitro degradabilities and digestibilities of dry matter and crude protein were determined in soybean meal treated with quebracho and chestnut tannin extracts. Chestnut tannins decreased the rumen crude protein degradability to a greater extent than quebracho tannins thus providing a greater amount of by‐pass protein.