Disclosed is a pharmaceutical composition for the treatment and prevention of periodontal diseases, comprising an extract from Rehmanniae Radix Preparata, Panax notoginseng (Burk.) F. H. Chen or a mixture thereof as an active ingredient. Having the activity of protecting the alveolar bone and promoting the proliferation of periodontal ligament cells as well as inhibiting the release of TNF-.alpha., the extract can be applied to the preparation of a pharmaceutical composition or a health food composition useful in the treatment and prevention of periodontal diseases.