Abstract: A photosensitive amphiphilic random copolymer P(VM-co-AMPS) was synthesized from 2-acrylanmido-2-methyl propane sulfonic acid(AMPS) and photosensitive monomer 7-(4-vinylbenzyloxy)-4-methyl coumarin (VM) by free radical copolymerization. P(VM-co-AMPS) self-assembled into colloid particles in the aqueous solution. The morphologies, sizes, and size distributions of the colloid particles were characterized by atomic force microscopy (AFM). The coumarin groups in the P(VM-co-AMPS) colloidal particles could be photodimerized and its photodimerization process was monitored using UV-Vis spectroscopy. Eventually, the P(VM-co-AMPS) colloidal particles were used as particulate emulsifiers to stabilize the toluene-in-water emulsions, observed by optical microscope. Results showed that the colloid particles possessed good UV absorption and emulsification properties. Preparation technology of self-assembled colloidal particles was simple and mild, avoiding the use of organic solvents.