Single-phase Pb1-xMnxS (0.03 ≤ x ≤ 0.37) nanoparticle films were prepared using an electroless solution growth technique. Face centered cubic structure with a decrease of lattice parameter for an increase of x in the alloy films was observed. Composition dependence of optical and electrical properties is discussed. The optical bandgap (Eg) could be varied from 1.50 to 2.50 eV by changing the x in the range 0.03 ≤ x ≤ 0.37 for the films. Effect of the grain size and the effect of alloying on optical properties are distinguished for the ternary nanoparticle films. Variable range hopping has been identified as mechanism for conduction in the p-type semiconductor Pb1-xMnxS nanoparticle films. Mobility μ of the majority carriers shows a decrease with increase in Mn concentration x and follows a T0.4 temperature dependence, indicating the surface scattering of carriers in the nanoparticle films. © 2006 The Electrochemical Society. All rights reserved.