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 is represented by Formula I: {[C ^N].sub.mM[P(R.sup.1R.sup.2)][LR.sup.3R.sup.4].sub.n}.sub.z (I). The cyclometalated transition metal complex can be employed in 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.