We have measured the complex dielectric function of Bi2Sr2CaCu2Oy, samples in the near infrared region directly by spectroellipsometry. As for both single crystal and thin film. superconducting samples have a zero point in the real part (ε1) of the complex dielectric function (ε*) and a clear peak of the imaginary part of the inverse ε* at almost the same frequency. On the other hand, non-superconducting samples have no such ε1, zero point, and the peak height of (-Im(l/ε*)) becomes small. Then we can determine the superconductivity of samples by this spectroellipsometry measurement at room temperature.