Here we present some results of our experimental study of the influence of a low gas pressure on the XeCl radiation efficiency in Xe-Cl2 mixtures pumped by a longitudinal glow discharge. When the pressure varied from 0.5 to 2 Torr the efficiency of XeCl radiation was shown to remain at the level of 10%. Maximum efficiency was obtained at a pumping power of 7x10–18 W per molecule with the spectral bandwidth increasing with gas pressure decrease reaching 12 nm at the pressure of 1 Torr. Processes involved in XeCl* molecule formation are discussed.