We estimate the survival probability of J/ψ in relativistic heavy-ion collisions, using both short-distance QCD and nuclear absorption mechanism. The suppression is found to be almost 100 percent for a thermally equilibrating quark-gluon plasma. The measurement of such a huge suppression of J/ψ may suggest the existence of a deconfined partonic medium, possibly a thermalised quark-gluon plasma, at RHIC.