Narrow-band PbS (Eg~0.4 eV) is widely used in optoelectronics as IR photodetectors, sensors, optical switches, gas-sensitive sensors. Doping PbS thin films with various metal ions, including rare earths, changes the structural and optoelectronic properties, and, consequently, the functional properties. The introduction of La3+ ions into PbS films has several effects. First of all, lanthanum ions can change the basicity of the surface of the lead sulfide film, which can increase its gas sensitivity. In addition, the recovery time of PbS films after contact with gas can be improved by doping with ions of the rare earth metal in question. This is due to changes in the structure and electronic properties of the film, which contribute to faster charge recombination. Thus, doping of thin PbS films with lanthanum ions can lead to an improvement in their functional properties, which makes such films promising for use in gas-sensitive devices, and La@PbS nanoparticles as photocatalysts and transistors. Most researchers prefer the preparation and doping of PbS films with lanthanum by spray pyrolysis. However, low-temperature chemical deposition of thin films of PbS(La) from aqueous solutions has significant advantages: simplicity, low cost, and the possibility of its implementation in industrial production. Among the existing methods for producing thin films, the method of chemical precipitation from aqueous media is the most technologically simple, which does not require expensive equipment due to relatively low synthesis temperatures. In order to search for optimal production conditions, this work carried out a preliminary analysis of ionic equilibria in the reaction system «PbAc2 - LaCl3 - Na3С6Н5О7 - NH4OH - N2H4CS», which made it possible to establish the concentration ranges for the formation of solid phases PbS and lead hydroxides Pb(OH)2 and lanthanum La(OH)3. Based on the selected recipe, light gray lanthanum-doped PbS films with a thickness of 480 ± 30 nm of n -type conductivity were obtained for the first time by chemical deposition at a temperature of 353 K for 90 minutes on glass substrates.