In order to improve the surface characteristics of polymethylmethacrylate (PMMA), oxide thin-film coatings were applied using the sol-gel dip-coating technique. The Si(OC2H5)(4) (TEOS), CH3Si(OC2H5)(3) (MTES) or Ti(O-i-C3H7)(4) (TIP) was used as a starting material for SiO2 or TiO2 coating. The hardness of the alkoxy-derived oxide-coated PMMA was increased from 200 MPa for non-coated PMMA with increasing film thickness. By optimizing the heating conditions and the hydrolysis conditions, and by repeating the dip-coating/heating processes, a hardness as high as 325 MPa was achieved in the PMMA triply coated with the TEOS-derived SiO2 film using the withdrawal velocity of 0.30 mm s(-1) and heat treatment at 80 degrees C. The increase in hardness with the thickness of coating film was saturated before reaching that of bulk silica-dried gel (ca. 500 MPa), which may be due to the increased porous nature of the thick films.