Electromodulation transmittance spectroscopy of CdS0.1Se0.9 nanocrystals embeded in the glass matrix is measured at room-temperature. Stronger electro-optical signals (10-4 - 10-3) are observed in both resonant and nonresonant regimes. These are some experimental results in resonant regime. The peak positions of electro-optical signals shift to higher energy direction when the nanocrystal size decreases;the line-shape of spectra for the same sample is independent of the external electric field strength;there are linear relationship between the signal magnitudes scale and the square of applied field strength, which indicates that the electro-optical effect of nanocrystals is the Kerr effect and the nanocrystals have the third-order nonlinear optical sus- ceptibility X(3);the signal magnitudes decrease when the modulation frequencies increase. The physical mechanism of resonant electro-optical effect is consistent with quantum-confined Stark effect. The oscillatory electro-optical signals in nonresonant regime are observed at frequency of 230Hz.The magnitudes of nonresonant electro-optical signal tend to enhangce with the increasing of the external electric field strength.The origin of nonresonant electro-optical effect is decreibed with "dielectric confinement"effect.