Cellulose acetate(CA) films containing anatase type titanium dioxide($TiO_2$) nanoparticles were prepared by solution casting. The film surface was modified by UV irradiation using a grid type UV irradiator. The UV irradiation caused slight increase in photodegradation of the CA films with $TiO_2$ compared to the CA film alone. However, CA films irrespective of $TiO_2$ content did not show a significant enzymatic degradation by a cellulase from Aspergillus niger without UV irradiation. Upon UV irradiation, the biodegradability remarkably improved even in the CA film without $TiO_2$. The irradiation of CA films decreased both the water contact angle and the degree of substitution(DS) implying the decrease in acetyl groups of the CA film surface due to the photo-scission of the acetyl group and photooxidation, resulting in more facile biodegradation of the surface film layer. The substantial enhancement in biodegradation of the UV irradiated CA film containing $TiO_2$ was attributed to the increased hydrophilicity, lowered DS and zeta potential due to the photoscission and the photooxidation effect of UV light. Also the increased surface area of the CA film due to the photocatalysis of $TiO_2$ particles may encourage the facile biodegradation.