NOVELTY - Method for preparing butyric acid by fermenting lignocellulose by using mixed flora, involves (a) preparing seed culture medium and a fermentation culture medium using mixture rich in cow dung, pig manure compost, cornfield soil and rotten wood, and pretreated rice straw, (b) inoculating the seed culture medium with the enriched flora and culturing, (c) inoculating the fermentation culture medium, and performing anaerobic fermentation, and (d) inoculating a slot type stirring reactor with the flora cultured in the step (c) for butyric acid fermentation.    USE - The method is useful for preparing butyric acid by fermenting lignocellulose by using mixed flora (claimed).    ADVANTAGE - The method enables to avoid excess use of cellulase, and is simple and cost-effective.    DETAILED DESCRIPTION - Method for preparing butyric acid by fermenting lignocellulose by using mixed flora, involves (a) preparing seed culture medium and a fermentation culture medium using mixture rich in cow dung, pig manure compost, cornfield soil and rotten wood (adopted as an initial flora) based on a peptone cellulose solution (PCS) culture medium, and pretreated rice straw as a raw material, (b) inoculating the seed culture medium with the enriched flora, allowing to stand and culturing four times, where the first time and second time culturing are performed at 35 degrees C for 14 days under anaerobic condition, the third time culturing is performed by inoculating 10 ml of second time cultured material, and culturing at 35 degrees C for 7 days under anaerobic conditions, and fourth time culturing is performed by inoculating 5 vol.% culture material and culturing at 35 degrees C for 7-15 days, (c) inoculating the fermentation culture medium with the flora cultured in the step (b), and performing anaerobic fermentation at 140 revolutions per minute (rpm) to obtain butyric acid, and (d) inoculating a slot type stirring reactor with the flora cultured in the step (c) for butyric acid fermentation. An INDEPENDENT CLAIM is included for method for preparing mixed flora, which involves collecting samples, placing in an enriched media collection containing rice straw as carbon source, adding a piece of filter paper in an enriched media as an indicator to completely disintegrated and obtaining as a standard, culturing for five months, and adding mixture rich in cow dung, pig manure compost, cornfield soil and rotten wood to culture medium, subculturing for 3 months to obtain original flora, where the samples are collected from cow dung, biogas sludge, manure, ditch sediment, cornfield soil and rotten wood.