$Cd_{1-x}Mn_{x}Te$ singe crystals were grown by the vertical Bridgman method and the Faraday rotations were measured as a function of wavelength and magnetic field. The Verdet constants were evaluated using the result of Faraday rotation. The Verdet constants were maximum at nearly absorption edge and increased for $0leq x leq 0.38 $ but decreased for x>0.40. We found that large Faraday rotation occur in $Cd_{0.62}Mn_{0.38}Te$ at nearly absorption edge wavelength was more useful for a magnetic field sensor than any other crystals, and $Cd_{0.60}Mn_{0.40}Te$ crystal was useful in this application when wavelength is He-Ne laser wavelength.