Some results of investigation of the UV (λ = 0.271 mm) copper vapor laser sum frequency (λ1 = 0.510 mm, λ2 = 0.578 mm) generation in nonlinear DKDP crystal are presented. For OOE interaction type the mean UV power of 0.2 W and conversion efficiency η of 3% have been reached when the mean power of nonpolarized radiation at the crystal input equals to 14 W. The efficiency η is shown to be essentially influenced by the beam divergence, pulse amplitude at both yellow and green lines, and by the delay between those pulses.