ZnSe single crystals were grown using the horizontal traveling solvent method (TSM) with selenium (Se) solution, The best FWHM of the X-ray rocking curve showed 26 arcsec and the lowest etch pit density was 1.4 x 10(5)/cm(2). The ZnSe crystals exhibited an I-1d peak in a photoluminescence spectrum, implying little unintentional doping of impurities. The relationship between the ZnSe crystallinity and the dissolution time of ZnSe source implies a small diffusion coefficient for the liquid Sc. The ZnSe molecule diffusion coefficient in liquid Se around 1060 degrees C was estimated to be (3.3 +/- 0.6) x 10(-10) m(2)/s, derived from the dissolution time. The small diffusion coefficient may be due to the slow movement of ZnSe molecules in an associated solution.