A novel mono-axial power spectrograph for spectral imaging ellipsometry is described in this paper. Spectral imaging ellipsometers employing the proposed mono-axial power spectrograph can measure information about thin films along the line of the entrance slit of the spectrograph. The mono-axial power spectrograph is simply composed of an entrance slit, a holographic transmission grating and a focusing cylindrical doublet. Several features of the proposed spectrograph give some benefits when used with an imaging ellipsometer. Above all, the holographic transmission grating guarantees polarization insensitivity of the incident wave to the spectrograph. Therefore, the polarization dependency and calibration factors in the spectral imaging ellipsometer can be minimized. Also, the simple structure of the spectrograph employing a cylindrical doublet allows optical compatibility with conventional ellipsometers and high adaptability to spectral imaging ellipsometers. The spectral resolution of the spectrograph is 5 nm and it has a spectral range from 400 to 800 nm. The focal length of the manufactured mono-axial power spectrograph is 25.4 mm and the total system dimension is less than 120 mm(L) × 100 mm(W) × 100 mm(H). The design procedure and the results of experiments to measure the spatial transmittance are discussed for some transmission samples.