The doping effects of Al3+ on the microstructure, magnetism, polar magneto-optical Kerr effects, and optical property of the sol-gel derived nanocrystalline CoFe2-xAlxO4 (x=0–1.0) thin films on silicon substrate were investigated. Doping of Al3+ not only led to the existence of two Kerr rotation peaks at 620 and 550 nm associated with the crystal-field transition, but also aroused the blueshifting of another peak at 540 nm correlated with the intervalence charge transfer transition. On the other hand, the reflectivity of as-deposited films increased with the Al3+ content x (except x=0.2) due to the decreased light scatter and absorptivity of Al3+ in substitution of Fe3+. Both the blueshifted Kerr effects and enhanced reflectivity in these films are of much benefit to magneto-optical recording. © 2003 American Institute of Physics.