The present invention relates to a Rehmannia glutinasa Libosch. extract for reducing blood glucose and lipid levels and treating hematologic diseases such as leukemia, and methods for preparing the same. The extract is prepared by subjecting fresh Rehmannia glutinasa Libosch. to flux extraction, concentrating the resultant extract, dissolving the concentrated extract with water, loading the obtained solution on a column packed with macroporous adsorption resins, eluting the column with ethanol, concentrating and drying the eluate. The extract can be made into clinically acceptable forms of dosage by pharmaceutically conventional measures, including capsule, tablet, pill, granule, dropping pill and so on. The extract is stable and has catalpol content up to 90-98%. The preparing method is simple to operate and applicable to industrial-scale production.
