A cyclometalated transition metal complex emitting phosphorescence of high efficiency and an organic electroluminescent display device employing the same are provided. The cyclometalated transition metal complex has a transition metal atom and a phosphorus ligand having at least one alkylene oxide and a phosphorus atom. The phosphorus atom is bound to the transition metal atom. The cyclometalated transition metal complex can be employed when forming an organic film of an organic electroluminescent display device, can emit light at a wavelength range of 400 nm to 650 nm, and can emit white light as well when used with a green light emitting material and a red light emitting material.