Passive pumping for lab-on-a-chip using surface tension only is the most effective method because the effect of surface tension on flow is significant in microscale. The movement of the triple point at a meniscus is driven by surface tension, resisted by viscous stress, and balanced by inertial force. In previous studies, the meniscus motion has been predicted theoretically with a one-dimensional model. However, three-dimensional flow field around the meniscus and the effect of cross-sectional shapes on the flow have not yet been assessed. Here, we visualized and analyzed the surface-tension-driven blood flow using spectral-domain Doppler optical coherence tomography.