The measurement on the mineral density (MD) of human tooth enamel with optical coherence tomography (OCT) is done, which is based on the linear relationship between the optical attenuation coefficient (OAC) and MD. Synthetic calcium hydroxyapatite discs (the key component of enamel) with different densities ranging from 1.28 g/cm3 to 1.9 g/cm3 are scanned with OCT, OACs are fitted from OCT images, and MD versus OAC curve as a calibration curve is developed; then the OACs within OCT images of human teeth are obtained; the MD is determined according to the calibration curve of OAC and MD. The MD of sound enamel is found to be 2.5~3.1 g/cm3, which is in agreement with literature values; while the MD of white spot lesions is around 2.0 g/cm3. This non-destructive method has the potential to be used in quantitative determination of demineralization and remineralization of enamel and clinic.