CdS nanoparticles have been formed within Langmuir-Blodgett (LB) films of cadmium salts of calix[8]- and calix[4]arene by reaction with hydrogen sulfide gas. The presence of CdS nanoparticles in the LB film matrices was checked by measurement of UV-vis absorption spectra, which allows an estimation of the size of the particles. It was shown that smaller particles (1.5 +/- 0.3 nm) are formed in calixarene LB films than in Cd stearate films (used for comparison). The particle size does not depend on the type of calixarene or the number of LB layers but increases with increasing pH of the subphase. The formation of CdS was directly confirmed with XPS.