In this paper, atmospheric-pressure plasma jet is used to prepare cobalt nanoparticles (CoNPs)withintwo period of times which are 10 and 12 minutes andhigh constant voltagesupplied by a 21kV power supplywith 3 L/min flow rate of argon and the frequency of 6 kHz of D.C. current.X-ray diffraction (XRD) spectrashowed of semi crystalline CoNPsand appearance of a number of different small peaks which observed at 2θ° with particle sizesof 52.987 in 10 minutes andof 48.478 nm in 12 minutes. Atomic force microscopy (AFM) was used to demonstrate the coordination of the synthesisedCoNPs, the average diametersof these particleswere 25.78 nm and 22.72 nm for 10 and 12minutes respectively, and showed a high extraordinary topographic contrast. Field Emission Scanning Electron Microscopy(FE-SEM) images demonstrated the topography and morphology of the produced CoNPs where the size of these nanoparticles formed ranged between 10-30 nm, also transmission electron microscopy (TEM) images revealed a homogenous CoNPs prepared in both preparation time (10, 12) minutes and clear that the formation of dispersed spherical nanoparticles resembles the interconnected grid