A new, common-path, in-axis concentric beam-splitting Michelson interferometer is demonstrated for optical coherence tomography (OCT), which can be used to perform high-resolution cross-sectional in vivo and in situ imaging of biological tissues. A piece of glass tube with its inner diameter smaller than the beam-width of the collimated light is used to split the light into a reference and sample beam. In order to obtain the optimal spectral interferogram of this OCT system, an infrared optical path adjustment method was introduced in this paper.