To develop genetic resources for microorganisms and to study the volatile fatty acid production by rice straw fermentation, mixed bacterial cultures FM_c, FM_d, FM_s, FM_w and FM_(d+w) were obtained by subculture with cow muck, pig compost soil, rotten wood, and mixture of pig compost soil and rotten wood as inoculums. Among the five mixed cultures, FM_w shows the highest straw degradation rate of 46.4%. The highest specific production rates of the total volatile fatty acid and the total butyric acid from rice straw are reached by the mixed culture FM_(d+w) with a value of 0.64 and 0.48g/g, respectively. The mixed culture FM_d produces more acetic acid from rice straw than others with a specific yield of 0.35g/g. It is found that the five mixed bacterial cultures all lack the acidity glucanase, resulting in a great restriction in the degradation of rice straw and the fatty acid yield. In order to improve the mixed cultures with respect to their fatty acid yield, a domestication to fatty acids and an optimization of cultivation conditions are desirable.