Optical coherence tomography (OCT) is a non-invasive high resolution cross-sectional imaging method with high sensitivity. A simple handheld spectral- domain optical coherence tomography (SDOCT) system is developed for imaging tooth tissues. The design of the handheld OCT probe is described in detail, and the lateral scanning is realized by using a scanning mirror. The handheld OCT probe is characterized by its compact size and portable feature, making it easier for in vivo tooth imaging. The system is used for imaging of in vitro and in vivo tooth tissues. The enamel, dentin and the interface between them can be clearly observed in the high-resolution tomographic images.