The behaviour of a sintered alloy Fe Mo 1.5 C 0.01 in two density states when subjected to an ion nitriding process is analysed. The thermochemical treatment was carried out with three different combinations of parameters (time, nitriding atmosphere). The analyses of the material after treatment included dimensional measurements, macro- and micro hardness determinations, diffractometric analysis and microstructural examination with an optical microscope and a scanning electron microscope equipped with an EDX system. All treatments led to satisfactory results for the material in the two density states: the volume mass is not a discriminative parameter in this case.