A series ef in vitro(2-stage fermentation) O.M. digestibility measurement was conducted to study the effect of maturity stage and location difference of some widely distributed native grasses in Korea. An attempt was also made to find the effect of fertilizer application on O.M. digestibility of Echinochola macrocarvi from July to late September. The results obtained were as follows; a) In vitro O.M. digestibility of native grasses studied decreased as the growing season progressed, from May to September. The rate of depression of digestibility was greater from May to June and from Aug. to Sept. than from June to Aug. It was concluded from the results that native grasses should be utilized before September. b) Eight different species of native grasses, including Themada japonica, Miscanthus purpurascens, Cymbopogon gaeringii, Lespedexa cuneata, Andropagan micrauthus, Digitaria Sanguinalis, Setaria viridis, and Phragmites prosturatus, collected from five different locations at middle of August showed different O.M. digestibility due to different locations. In general, lower digestibility was obtained with the species collected from Alpine area. c) Fertilizer application of Echinochola macrocorvi depressed O.M. digestibility when compared to that of non-fertilized plot, except early growing stages. However, total digestible organic matter production was greater with fertilized than non-fertilized.