Mn/O nanoparticles were prepared by laser heating gas evaporation method in this paper, with a 150 W CW CO 2 laser as light source and Mn(Ac) 2·4H 2O as a target. The effects of process parameters on nanoparticles have been pilot studied. XRD, DTA and TEM were used to characterize the samples. The formation mechanism of Mn/O nanoparticles was preliminarily discussed. The experimental results show that the process parameters such as laser power density, reaction pressure, the sorts and rate of airflows et al., effect the sizes and crystal system of nanoparticles., The products are Mn 3O 456F, the diameter of nanoparticles is between 5～10 nm and 30～100 nm in Ar atmosphere. The products are Mn 3O 4 and MnO and the diameter of nanoparticles is between 5～10 nm and 15～60 nm in O 2 atmosphere.