Two in vitro methods were compared to select convenient one for further practical application in the fields of evaluation of nutritive value of feedstuffs and rumen metabolism. The CO₂ gassing system was found statistically superior to the Bunsen valve system during the first stage of fermentation period. The Tilley and Terry method modified by Lee was found slightly higher organic matter digestibility than original Tilley and Terry method with alfalfa hay sample, but a decreased in vitro organic matter digestibility was found with barley straw. The method modified by Lee was applied to introduce a linear regression equation, Y=0.99x-1.8, between in viva and in vitro organic matter digestibilities using some New Zealand feedstuffs.