Aims: This study was developed to purify and to characterize a keratinolytic protease from the bacterium Microbacterium sp. strain kr10. Methods and Results: Enzyme purification was carried out by sequential liquid chromatography on Sephadex G-100 and Q-Sepharose columns. The purification was about 255-fold, with a yield of 34%, as determined with azocasein as substrate. The molecular weight of the enzyme was estimated as 42 000 Da by SDS-PAGE. The enzyme had pH and temperature optima of 7(.)5 and 50 degrees C respectively. This keratinase was inhibited by EDTA and 1,10-phenanthroline, and analysis of metal content indicates that Zn2+ and Mg2+ are present. A 2(2) factorial design was developed to investigate the effect of keratinase and mercaptoacetate concentration on feather keratinolysis. Statistical analysis showed that both variables have a significant effect on hydrolysis of keratin. Conclusions: A new keratinase produced by Microbacterium sp. was purified and characterized. Significance and Impact of the Study: This keratinolytic enzyme offers an interesting potential for the hydrolysis of keratin wastes to be used as feed supplement or bioconversion to added-value products.