Polymethyl methacrylate - boehmite nanocomposites (PMMA-x-BNCs; where x = 10.0 and 20.0 wt % of PMMA nanoparticles in the latexes) were synthesized by a procedure in two steps. Firstly, polymethyl methacrylate nanoparticles (PMMA-NPs) were prepared either without or with the addition of divinyl benzene as cross-linking agent by semicontinue-direct microemulsion polymerization. Secondly, PMMA-NPs were added to aluminum sec-butoxide solution to obtain PMMA-x-BNCs, by the in-situ sol-gel preparation method. The PMMA-x-BNCs samples were annealed at 300 degrees C for 4 h and characterized by X-ray diffraction (XRD), electron transmission microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), N-2 physisorption, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopies. The PMMA-x-BNCs nanocomposites, mainly those containing cross-linked PMMA-NPs showed enhanced absorption of UV and visible light. The band gap energy (E-g) of PMMA-x-BNCs decreased to a level comparable to that of a semiconductor material. The carbon residues and the remaining carbonyl group of PMMA after the annealing process promoted the improvement of the specific surface area, the decrease in the E-g and the inhibition of the recombination rate of electron-hole pairs.