A biopsy is a well-known medical test used to evaluate tissue abnormality. Biopsy specimens are invasively taken from part of a lesion and visualized by microscope after chemical treatment. However, diagnosis by means of biopsy is not only variable due to depth and location of specimen but may also damage the specimen. In addition, only a limited number of specimens can be obtained, thus, the entire tissue morphology cannot be observed. We introduce a three-dimensional (3-D) endoscopic optical biopsy via optical coherence tomography employing a dual-axis microelectromechanical system scanning mirror. Since this technique provides high-resolution, noninvasive, direct, and multiple visualization of tissue, it could function as a clinical biopsy with advanced performance. The device was integrated with a conventional endoscope and utilized to generate in vivo 3-D clinical images in humans and animals.