Abstract: For understanding the biodegradable properties of chrome-free leathers, the Penicillium sp. was used to degrade vegetable tanned and aldehyde tanned hide powder. The changes of hide powder structure and thermal properties during the degradation were analyzed by Scanning Electron Microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), Thermo Gravimetric Analyzer (TG), Differential Scanning Calorimetry (DSC) and Micro Hot Table (MHT). The degradation degree of hide powder was characterized by the contents of hydroxyproline and total nitrogen in the filtrate. The results showed that the both kinds of tanned hide powder were degraded by the Penicillium sp. The surface morphology and structure of hide powder were destroyed, the property of thermal stability and thermal-decomposition resistance were reduced. Penicillium sp. had more obvious effect on reducing thermal stability of vegetable tanned hide powder, but the thermal-decomposition resistance of aldehyde tanned hide powder was further damaged during degradation process. The pH and nutrition component were changed during degradation process, so the degradation degree slowed down. As vegetable tanned leather was more sensitive to pH, more drastic detanning caused by pH changing resulted in better degradation effect. In sum, the chrome-free leather degradation was a synergistic effect of detanning and Penicillium sp.growth.