This paper presents two techniques based on optical coherence tomography, the “focus tracking method” and the “optical path shifting method,” for determining refractive index and thickness simultaneously, which are especially useful for bio tissues. From comparison of these two methods, it was found that the focus tracking method is suitable for in vivo measurement, but does not have high precision. The optical path shifting method is limited to in vitro measurement, but has high precision. Using the optical path shifting method, the refractive indices of cucumber were measured at the wavelength of 850 and 1300 nm. © 2002 Society of Photo-Optical Instrumentation Engineers.