Abstract: The optical constants of YVO4 crystal in the frequency range of 0.2 to 1.0 THz were determined using terahertz time-domain spectroscopy. The extraordinary-ray refractive indices varied from 4.05 to 4.07 and the ordinary-ray refractive indices were approximately 3.07. We found that YVO4 crystal had a large and nearly constant birefringence of ~0.985. In addition, the power absorptions for YVO4 were less than 7 cm-1. Our results indicated that YVO4 crystal has a potential for applications in the THz frequency range.