This study was carried out to investigate the effect of replacement of wheat straw by different levels of maize cobs in composite ration on in vitro degradation of dry matter, truly digestible organic matter and production of microbial biomass in order to determine its level of supplementation in ruminant ration. Wheat straw was replaced by maize cobs @ 0, 10, 20, 30, 40, 50 and 100% level to formulate composite rations. The different formulae of composite rations were used for in vitro gas production studies using goat rumen liquor with wheat straw. In physical treatment only soaking was done while under chemical treatment application of urea, molasses and combination of both urea and molasses were applied before conducting in vitro studies using goat rumen liquor. Proximate composition, fi ber fractionation and calcium and phosphrous content of all the composite rations were estimated. The in vitro degradability of maize cobs based diets is better than wheat straw based composite ration. There was no signifi cant (P>0.05) improvement in per cent IVDMD of maize cob based diet by water soaking irrespective of the soaking period, however, a signifi cant (P<0.05) improvement in in vitro degradation parameters were observed with urea-ammoniation of maize cobs. No benefi t of molasses treatment either in isolation or in combination was observed over maize cobs utilization as compared to urea-ammoniated maize cobs. It is concluded that feeding value of maize cobs is similar to wheat straw as indicated by IVDMD while urea-ammoniation appears to be the ‘treatment of choice’ for improving nutritive value of maize cobs.