The feed value of Astragalus membranaceus leaves and straws was amended by fermentation using effective microorganisms, such as molasses (T1), Rhodobacter capsulatus (T2), Bacillus subtilis (T3), Lactobacillus acidophilus (T4), or Saccharomyces cerevisiae (T5), with no supplements in the control (C). The crude protein (CP), ether extract (EE), crude fiber (CF), neutral detergent fiber (NDF), and acid detergent fiber (ADF) contents in the fermentation-treated A. membranaceus leaves decreased, whereas nitrogen free extract (NFE) content increased significantly. A decrease in the amounts of CP (except in T3), EE, CF, NDF, and ADF in the A. membranaceus straws treated with effective microorganisms was observed compared with that for the C and T1 (p<0.05). The NFE content of the straws increased with all treatments, except T1. Fermentation treatment subtly altered the fatty acid composition of A. membranaceus leaves and straws. In contrast, the calcium and vitamin E contents in A. membranaceus leaves and straws were increased after fermentation treatment (p<0.05). However, T3 yielded higher saponin content in straws compared to that by any of the other treatments (p<0.05). The effect of fermentation with microorganisms, maintained the low pH up to 48 h (p<0.05), whereas it was random for the straws. Therefore, the data suggest that fermentation treatment with microorganisms can improve digestion rate and have a positive effect on physiologically active substances and feed value.