Nanometer-size carbon particles were prepared on a Si substrate using pulsed laser deposition (PLD) assisted by radio frequency (RF) Ar plasma and were compared with ones prepared by PLD in vacuum and Ar gas. In both the plasma and gas ambiences, experiments were carried out in Ar pressure p(Ar) ranging from 0.13 to 13 Pa. The particle size increased as p(Ar) increased. However, the size obtained in the RF Ar plasma was approximately 1.5 times larger than that prepared in the Ar gas. An X-ray photoelectron spectroscopy (XPS) analysis revealed that the carbon film covered by the particles was in an amorphous state. The sp(3)/sp(2) carbon ratio of the film was evaluated by deconvolution of XPS carbon (Is) spectra into three components, which are attributed to diamond (sp(3)), graphite (sp(2)) and carbon oxide components. The highest sp(3) /sp(2) ratio was 0.4 in the Ar gas and Ar plasma at p(Ar) = 0.13 Pa. The sp(3) /sp(2) ratio decreases monotonously, as the particle size increases. The ratio obtained in the Ar plasma is larger than that in the Ar gas. The effects of p(Ar) and plasma for nanoparticle characteristics are discussed.