Effects of the amount of activated carbon, temperature, adsorption time and stirring speed on the decolorization of oligosaccharide extract from Rehmannia were investigated by orthogonal experimentsThe optimal conditions were as follows, 6% of the amount of activated carbon (weight/weight, activated carbon/Rehmannia) and stirred at 80 r/min and 80°C for 30 min.The average content of stachyose and the average removal rate of impurities were 62.97% and 82.33%, resp.