CdSe nanoparticles have been prepared by ultrasonic assisted ionic liquid method and characterized by XRD, SEM and fluorescence spectroscopy. XRD spectrum demonstrates the product is a cubic phase of well–crystallized CdSe and the crystallinity increases with increasing reaction time. The effects of ionic liquid of [Bmim]OH–H2O and reaction time on microstructure and fluorescence of the CdSe were studied. The diameter of CdSe nanoparticles synthesized in 1 ml [Bmim]OH–H2O solution (ultrasonic irradiation, 1 h)is 30-60 nm and fluorescence intensity achieves 54 a.u.. CdSe nanoparticles could be enhanced by the method of being coated with ionic liquid to prevent the aggregation of nanoparticles.