The dried roots of Rehmannia glutinosa (RG) have been used in the traditional medicine for treatment of diabetes, fever and dysuria, etc. In order to investigate the quality evaluation of the dried roots of RG, we conducted the physico-chemical and biological evaluation method. The amount of catalpol from commercial samples is very diverse about $0.00{sim}3.89%$ by using HPLC method, because it is easily decomposed by processing of RG. So, we should try to identify the correlation with the contents of catalpol and biological activities of RG. We chose 3 samples which were a wide difference of catalpol contents between each sample (Sample-I; 3.4%, Sample-II; 2.8%, Sample-III; 0.05%). Sample-I and Sample-II were found to be more effective than Sample-III on the DPPH free radical scavenging effect and inhibitory effect on $H_2O_2-catalyzed$ lipid peroxidation in rat liver in vitro. And, Sample-I and Sample-II exhibited more significant effects than Sample-III on accelerating actions of the small and large intestinal transport, and diuretic action in mice. So, it is suggested that the quantitative determination of catalpol should be required for the tandardization of the dried roots of RG.