Indium hydroxy sulphide thin films have been deposited from an acidic bath using indium (III) chloride, thioacetamide and acetic acid as complexing agent. It has been found that the proper control of deposition conditions significantly influences the film quality and reproducibility as well as the film thickness. XPS measurements have been carried out for samples prepared using different reactant concentrations in order to study variations in the surface composition. Some films have been also air-annealed at 300 and 400 degrees C to know in which way the composition is affected by this processing. Films are formed by indium hydroxy sulphide, indium oxide and indium sulphate having contaminant species adsorbed on the surface. All samples annealed have shown an oxygen incorporation from the air and an important sulphur loss. The S/In atomic ratio in the indium hydroxy sulphide compound is about one for the non-annealed samples showing that the compound is sulphur deficient. When samples are annealed at 400 degrees C, this value is decreased down to 0.3 owing to the formation of sulphur containing volatile species. The molecular formula for the indium hydroxy sulphide as deposited can be close to InOHS with slight variation in the OH:S proportion depending on the deposition conditions and the annealing temperature.