Successful synthesis of alloy nanoparticles is deemed to be an important step toward realizing applications of different alloy nanoparticles. The preparation of alloy nanoparticles is primarily attempted using physical route with scarce examples of using chemical route of preparation. Efforts are made, for the first time, to synthesize Pb-In alloy nanoparticles via solvothermal route. The present investigation deals with the systematic study of the effect of processing parameters on the formation of Pb1-xInx (x = 0.44, 0.64, and 0.80) alloys in solvothermal route. The results indicate that the formation of alloy [FCC (Pb)] nanoparticles is strongly dependent on the molar ratio of precursor to reducing agent (1:1–1:3), temperature (100–140°C), time (2–4 h) and capping agent (1:5–1:10). Different morphologies of the product such as spherical, cube-octahedral nanoparticles as well as nanosheets have been observed depending on the concentration of the reducing and capping agents. The systematic study allows us to develop a model on alloy formation.