High doping efficiencies have been observed in phosphorus-implanted CuInS2 single crystals by pulsed electron-beam annealing, which could not be achieved by the conventional furnace annealing method. This paper presents the investigations by using the electron paramagnetic resonance measurement on this p-type doping effect. The electron paramagnetic resonance signal from the phosphorus interstitials was observed in the as-implanted crystals. The same signal appeared in the subsequently thermally annealed samples but disappeared in the pulsed electron beam annealed ones. This shows the superiority of melting crystal surfaces in the pulsed electron-beam annealing on eliminating the implantation-induced defects to obtain high doping efficiencies.