In order to analyze the changes in the contents of Rehmanniae Radix during processing, the constituents of Rehmanniae Radix Preparata, such as catalpol, 5-HMF and the carbohydrates, were analyzed, The results were: 1. The catalpoI contents of Rehmanniae Radix Preparata remarkably decreased during the 1-4th steps in the processing, and the concentrations of 5-9th Rehmanniae Radix Preparatas were very low. 2. The contents of 5-HMF increased gradually with each additional processing. and the increasing rate in oven-dried Rehmanniae Radix Preparata was greater by about 2-folds than that of sun-dried. 3. Rehmanniae Radix contained a lot of sugars. such as rhamnose, raffinose and stachyose. In the course of the process for sun-dried or oven-dried Rehmanniae Radix Preparata., rhamnose disappeared during the 1-2nd step, but raffinose and stachyose stayed the same. 4. The level of fructose, developed at the first processing step, stayed the same during each additional processing for sun-dried Rehmanniae Radix Preparata. But, the level gradually decreased after the 6th processing step for oven-dried Rehmanniae Radix Preparata.