We report the first example of diluted magnetic semiconductor (DMS) fine particles incorporated into Langmuir-Blodgett (LB) films. Cd1-xMnxS (x = 0.45, 0.27 and 0.20) fine particles with about a 3-nm diameter were prepared through the reaction of arachidate LB films containing Cd and Mn with hydrogen sulfide (H2S) in an atmosphere of NH3. Electron spin resonance (ESR) measurements, before and after H2S treatment, gave information on the microstructural changes which occurred in the film during particle formation. The anomalous broadening of the line shape and the anisotropic properties of quasi two-dimensional magnets were observed before H2S treatment, while, after H2S treatment, these characteristic features completely disappeared, and a typical exchange-narrowed line arose. The drastic changes observed here indicate that Cd1-xMnxS fine particles were produced in a spherical shape, not in a two-dimensional sheet.