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Abstract: The in situ electrochemical deposition of nanostructured MoS x (x =1.5–1.7) based thin films on various substrates from aqueous solutions is reported. The as-deposited amorphous films transform on annealing into crystalline ones as revealed by a stepwise high temperature X-ray diffraction (XRD). Both Raman spectroscopy and XRD crystal structure analyses confirmed the formation of inorganic fullerene-MoS x nanoparticles (IF-MoS x ). The as-deposited thin films have a featureless surface morphology, but after annealing either a nanotube or a nanorod structure along with numerous smaller nanoballs appear at the surface. An investigation by transmission electron microscopy unearths the presence of nanoballs, nanoribbons, and nanotubes throughout the annealed MoS x thin films. The size of the nanoballs is in the range of 5–10nm. The nanotubes have a diameter of 10–400nm, and a length of up to several micrometers as evidenced by SEM. The catalytic effect of transition metals on the growth of nanotubes is noticed. The temperature-induced transformation from amorphous to crystalline structured MoS x films results in a large lowering of the coefficient of friction under sliding against corundum in ambient air of 50% relative humidity. [Copyright &y& Elsevier]