The applicability of the alkaline extraction method using a 5% potassium hydroxide (KOH) solution to predict organic matter digestibility (DOM) of ruminant feeds was examined. The predictive value of the assay was estimated using 110 feeds including dried grass (70), grass silages (33) and compounds (7) of known DOM determined on sheep (DOM_v). A fairly close linear relationships for all samples and forages between the in vitro organic matter digestibility (DOM_k, X, %) and DOM_v (Y, %) estimates were found. The regression equation for all samples (n= 110) was Y = 0.934 X + 5.74, R² = 0.75 (P<0.001), residual standard deviation RSD 3.65, for all forages (n= 103) Y = 0.903 X + 7.67, R² = 0.67 (P<0.001), RSD 3.62. The regression of DOM_v on DOM_k for compounds (n = 7) was insignificant (R² = 0.30, RSD 3.74). The relationship between DOM_v (determined values) and DOM_vk (predicted from the equation for all samples) was linear. The predicted values could account for 75% of the variance in determined DOM_v; RSD = 2.52. The residuals (DOM_v - DOM_vk) were correlated with DOM_v (r = 0.51, P<0.001). DOM_vk tended to be overestimated for samples of DOM ranging 50-60% (negative residuals only) and underestimated for that of DOM exceeding 80% (positive residuals only). The most even distribution of the residuals was in the DOM range of 70-80%.