We investigated a high-precision optical method for measuring the thickness of biological samples regardless of their transparency. The method is based on the precise measurement of optical path length difference of the end surfaces of objects, using a dual-arm axial-scanning low-coherence interferometer. This removes any consideration of the shape, thickness, or transparency of testing objects when performing the measurement. Scanning the reference simplifies the measurement setup, resulting in unambiguous measurement. Using a $1310\mathrm{nm}$ wavelength superluminescent diode, with a $65\mathrm{nm}$ bandwidth, the measurement accuracy was as high as $11.6\mathrm{\mu m}$ . We tested the method by measuring the thickness of both transparent samples and nontransparent soft biological tissues.