Herein, we report the ambient synthesis of CdSe nanoparticles of widely tunable particle size by a solution route. The proposed protocol uses hydrazine hydrate to form an air-stable complex of selenium. These nanoparticles are characterized by X-ray diffraction, FTIR, optical absorption, photoluminescence, and transmission electron microcopy measurements. By varying the molarities of Cd2+ and Se2- ions in solution with 3-mercaptopropionic acid as the capping ligand, the method permits us to synthesize nanoparticles of size ranging from 1.58 to 3.42 nm (estimated from optical absorption edge measurements) by controlling the annealing time of the starting colloid at 100 degrees C. The extracted quantum dots are of high quality (40% photoluminescence quantum yield) and exhibit colors ranging from deep blue to red. The resulting colloids arc very stable. and no precipitate is observed over it period of 6 months. Thus, the method is simple and easily scalable to synthesize fluorescent. CdSe nanoparticles.