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Nickel oxide nanoparticles were fabricated by a laser ablation technique using the third harmonic of an Nd:YAG laser and sintered NiO targets in an on-axis configuration under argon pressures of 0.67, 1.33, and 2.00 Pa. The effects of the number of irradiating laser pulses, gas pressure, and target-to-substrate (T-S) distance on the average particle size, size distribution, and particle areal density were investigated. The nanoparticles obtained were always crystalline and 2 to 6 nm in diameter, irrespective of the preparation conditions as determined by high-resolution transmission electron microscopic (HRTEM) analysis. The average particle size increased with the number of laser pulses, indicating the particle growth on the substrate. The particle areal density was strongly affected by the target-to-substrate distance. The formation process of the nanoparticles is also discussed.