Functional polymeric membranes are widely used to adjust and control the diffusion of mols. Herein, photosensitive poly(hydroxycinnamic acid) (PHCA) microspheres, which were fabricated by an emulsification solvent-evapn. method, were embedded into an Et cellulose matrix to fabricate composite membranes with a photo-tunable property. The photoreaction of PHCA is based on the [2 + 2] cycloaddn. of cinnamic moieties upon irradn. with 365 nm light. Intra-particle crosslinking in PHCA microspheres was confirmed in the soln. phase, while inter-particle crosslinking between adjacent PHCA microspheres dominated the solid membrane phase. The inter-particle crosslinking turned down the permeability of the composite membranes by 74%. To prove the applicability of the designed system, the composite membrane was coated on a model drug reservoir tablet. Upon irradiating the tablet with UV light, the original permeability decreased by 57%, and consequently the diffusion rate of the cargo (Rhodamine B) from the tablet slowed down. Most importantly, the tablet showed sustained release for over 10 days. This controllability can be further tuned by adjusting the membrane thickness. Composite membranes showed excellent processing reproducibility together with consistent mech. properties. These results demonstrate that the incorporation of photosensitive PHCA microspheres in polymeric membranes provides a promising photo-tunable material for different applications including coating and sepn.