Beef marbling is known as one of the most important beef-quality traits in Korea. It is likely that marbling derived from fatty acids, mainly propionate, is mediated by rumen. Recently micro-agents were studied to enhance marbling, although many parts of that were digested in rumen. Therefore, this study was conducted to screen candidate materials to effect on beef quality with in vitro ruminal incubation. The materials such as saponin, chitosan, Zn compounds (4), vitamin C sources (2), Korean herb cocktail and garlic sources (2) were added to rumen fluid to 1.25% of substrate volume at 0 and 24 h incubation time. Total gas production in intact vitamin C source increased but that in all Zn compounds decreased (P＜0.05). Total gas production in Zn sulfate compound less decreased than in other Zn sources. Propionate in Zn sulfate increased than the other candidate compounds at all incubation time (P＜0.05). Experiment two was conducted to clarified effect of additives such as vitamin C sources (2), garlic lyophilized, Korea herb cocktail and Zn sulfate were supplemented with 2.5% volume at the 0, 3, 6, 12 and 24 h incubation time. Total gas in Zn sulfate was lower than any other treatments. Propionate in garlic, herb and Zn sulfate appeared to be lower than control and vitamin C sources at all incubation time, although significant difference was not observed in total VFA among control and all treatment. This study suggested that micro-agent might be used to improve beef quality with minute level.