An investigation was made of the efficiency of a laser utilizing a concentrated Li-Nd-La phosphate glass as the active medium and an LiF crystal with F//2** minus centers as a passive Q switch. The efficiency was about 0. 5% in the pump energy range 5. 6-13 J and the distribution of the output radiation corresponded to the TEM//0//0 mode. The main factor which limited the output energy of the laser pulses was the partial filling of the aperture of the glass active element. The experimental results were compared with calculations. Relationships were obtained for estimating the values of the parameters of the output pulses obtained under various experimental conditions. Estimates were obtained of the influence of the residual and induced absorption, and of the relaxation time of the passive switch on the lasing efficiency.