This experiment examined effects of adding cellulase or lactic acid bacteria (LAB) on silage fermentation and in vitro gas production of various morphological fractions of maize stover. Maize stover was separated into leaf blade, leaf sheath and whole stem, or kept as whole maize stover, and each fraction was ensiled for 60 days with 0, 10 and 20 ml of cellulase or 0, 105 and 2 × 105 cfu/g LAB, per kilogram of wilted material. The silage was sampled for measurement of pH, lactic acid, chemical composition and in vitro gas production. Before ensiling there were substantial variations in chemical composition between the fractions of maize stover (P<0> whole maize stover > leaf sheath > leaf blade. Losses of dry matter (DM) and aNDF were in the order: leaf blade > leaf sheath > whole maize stover > whole stem. Addition of either cellulase or LAB accelerated (P<0>