A microelectromechanical system (MEMS) mirror based endoscopic swept-source optical coherence tomography (SS-OCT) system that can perform three-dimensional (3-D) imaging at high speed is reported. The key component enabling 3-D endoscopic imaging is a two-axis MEMS scanning mirror which has a mirror plate and a device footprint. The diameter of the endoscopic probe is only 3.5 mm. The imaging rate of the SS-OCT system is . OCT images of both human suspicious oral leukoplakia tissue and normal buccal mucosa were taken in vivo and compared. The OCT imaging result agrees well with the histopathological analysis.