The Faraday rotation of Cd0.8Mn0.2Te and Cd0.9Mn0.1Te single crystals grown in our laboratory was measured at room temperature. We analyzed our Faraday rotation data in terms of a modified multi-oscillator model by improving the value of the band gap at L point in the Brillouin zone (E1) and obtained the values of the gap at the Γ point in the Brillouin zone (E0) for Cd0.8Mn0.2Te and Cd0.9Mn0.1Te from the fitting to 1.667 eV and 1.804 eV, respectively. The values of E0 are more close to the calculated ones than nearly all of the previous studies.