On- chip UV-polymerization to synthesize polystyrene (PS) microparticles is carried by a simple microfluidic device. The PS microdroplets could be cured insitu in microfluidic device. The obtained microparticles using microfluidic approach could have various size of diameter (130 and 200 µm) by adjusting flow rates of continues and dispersed phases as well as viscosity of continue phase.