We present the design of two efficient micromixers, a 3-D serpentine micromixer and a vortex mixer. Light and confocal microscopy and image analysis programs were used to study mixing efficiency in these two micromixers and a Y-shape straight channel. By utilizing Optical Coherence Tomography (OCT), an emerging high-resolution medical and biological imaging technology, we obtained 3-D structural data and mixing dynamics for the 3-D serpentine mixer and the vortex mixer. The results indicate that mixing efficiency characterized with OCT is more accurate.