In order to achieve effective process control, the fast, inexpensive, nondestructive and accurate nanoscale feature measurements are extremely useful in high-volume nanomanufacturing. The optical scatterometry has currently become one of the important approaches for in-line metrology of geometrical parameters of nanostructures in high-volume nanomanufacturing due to its high throughput, low cost, and minimal sample damage. Conventional scatterometry techniques can only obtain the mean geometrical parameter values located in the illumination spot, but cannot acquire the microscopic variation of geometrical parameters less than the illumination region. In addition, conventional scatterometry techniques can only perform monospot test. Therefore, the sample stage must be scanned spot by spot in order to obtain the distribution of geometrical parameters in a large area. Consequently, the final test efficiency will be greatly reduced. Accordingly, in this paper, we combine conventional scatterometry with imaging techniques and adopt the Mueller matrix imaging ellipsometry (MMIE) for fast, large-scale and accurate nanostructure metrology. A spectroscopic Mueller matrix imaging ellipsometer is developed in our laboratory by substituting a complementary metal oxide semiconductor camera for the spectrometer in a previously developed dual rotating-compensator Mueller matrix ellipsometer and by placing a telecentric lens as an imaging lens in the polarization state analyzer arm of the ellipsometer. The light wavelengths in the developed imaging ellipsometer are scanned in a range of 400-700 nm by using a monochromator. The spectroscopic Mueller matrix imaging ellipsometer is then used for measuring a typical Si grating template used in nanoimprint lithography. The measurement results indicate that the developed instrument has a measurement accuracy of better than 0.05 for all the Mueller matrix elements in both the whole image and the whole spectral range. The three-dimensional microscopic maps of geometrical parameters of the Si grating template over a large area with pixel-sized lateral resolution are then reconstructed from the collected spectral imaging Mueller matrices by solving an inverse diffraction problem. The MMIE-measured results that are extracted from Mueller matrix spectra collected by a single pixel of the camera are in good agreement with those measured by a scanning electron microscope and the conventional Mueller matrix ellipsometer. The MMIE that combines the great power of conventional Mueller matrix ellipsometry with the high spatial resolution of optical microscopy is thus expected to be a powerful tool for large-scale nanostructure metrology in future high-volume nanomanufacturing.