In endoscopic elastography, it is needed to observe small area with high spatial resolution. Optical coherence tomography (OCT) is one of the candidate imaging methods, which has the depth resolution of several∼10 μm. In this study, we try to find the propagation velocity of surface acoustic wave (SAW) using a swept-source OCT (SS-OCT). The depth scanning rate in the SS-OCT is rather fast, which is determined by the wavelength sweep of the light source as fast as 20-100 kHz. However, on the other hand, the lateral scanning is limited up to 100 times per second, since it is performed using a mechanical moving mirror. We develop a theory to estimate SAW velocity of tissues ranging from 1 to 20 m/s from data taken by the slow lateral scanning of less than 1 m/s using the OCT. The present method is tested for agar samples with different concentrations and also for several tissue samples. Vibrations are excited on the sample surface using a small stick connected to a loudspeaker. The measurements are carried out at many frequencies from 500 Hz to 1000 Hz. The dependence of the SAW velocity on the concentration successfully agreed the previous results. © 2013 Acoustical Society of America.