In animal testing, abdominal injection of commercial fulvic acid (FA) to Wistar rats resulted in the coloration of the bone. Free radical signal was detected by ESR spectra of the bone, which were shown to be dependent upon the dosage of FA injected. The fluorescence spectra, UV spectra and gel permeation chromatography of the alkaline extracts of the bone showed similar characteristics to FA. In in-vivo rat tests and in-vitro experiments of cultured chicken cartilage tissue with tritium labeled FA, the results showed that 3H-FA could be incorporated into the bone and cartilage of rats.