Abstract: A composite biosorbent was prepared by mixing four microbial biosorbents from absorption groups with diverse characteristics.The Cr(Ⅲ) adsorptive property of the composite biosorbent was tested in low Cr(Ⅲ) mass concentration solution by statistical method.The Plackett-Burman (P-B) design and Response Surface Methodology (RSM) were applied to optimize the adsorption process based on single factor experiments.The P-B results showed that the pH,initial Cr(Ⅲ) mass concentration,dosage of biosorbent XB and TQ were the four main factors that significantly affected the adsorption process.The path of steepest ascent was undertaken to approach the optimal region of the four significant factors.A second order model of the adsorption of low Cr(Ⅲ) mass concentration was obtained by Box-Behnken design and response surface analysis.Results indicated that the optimal adsorption condition of pH,initial Cr(Ⅲ) mass concentration,microbial biosorbents XB and TQ concentration were 4.0,4.86 　mg/L,0.20 and 0.13 g/L,respectively.The results of verification testing showed that the optimized adsorption rate was 87.54%,very close to the predicted value of 87.68%,and the absorptive was rate higher than that of a single biosorbent by 7.79%-17.35%.FT-IR spectra photography revealed that the improved adsorption capability was related to the increase of functional groups in composite biosorbents.The sorption characteristics of the composite biosorbent will obviously be enhanced if Response Surface Methodology (RSM) were applied to optimize the adsorption process.