Mn1.56Co0.96Ni0.48O4 (MCNO) thin films with different thicknesses ranging from 180 nm to 600 nm were deposited onto a SiO2/Si(1 0 0) substrate at 600 degrees C by using the chemical solution deposition method. The thickness dependent structural and optical properties of the MCNO films were investigated in this study. As identified by the SEM pictures and X-ray diffraction (XRD) spectra, all samples showed polycrystalline cubic spinel structure, and the stoichiometric status is improved with growing thickness according to XRD results. Spectroscopic ellipsometry spectra were measured in this study to investigate the thickness dependent optical properties of MCNO film in the range of 300-1000 nm. The samples showed three absorption structures locating at 1.6-1.9 eV, 2.6 eV, and above 3.5 eV, corresponding to the charge transfer transition involving 2p orbitals of O2- and 3d orbitals of Mn and Co ions, respectively. The absorption structure at above 3.5 eV decreases gradually as the thickness grows, while the peak around 1.6-1.9 eV weakens slightly before it enhances again with film thickness above 430 nm, which can be explained by a combined effect of crystallinity improvement and increase in Mn4+/Mns+ ratio.