The phase-matching angle, effective nonlinear coefficients, walk-off angel and angular bandwidth are calculated. High pulse energies of nanosecond level fourth-harmonic generation of a Ncì:Yalt laser have been obtained with CsLáB(1Oio nonlinear crystal. 50 mJ of 266 nm output with a conversion efficiency 40% from the second-harmonic input was generated. The properties of effective frequency conversion in a new nonlinear crystal-CsLiBdOш are discussed.