Nowadays, due to the useful and unique properties of magnetic nanoparticles, their use in various sciences has been considered. Spinle ferrite nanoparticles are of particular importance. Because the great impact of the synthesis techniqe, dopping, and coating on the magnetic properties of nanoparticles,they are being investigated by researchers to achieve the practical objectives of the above factors. There are different fabrication methods, depending on the manufacturer's purpose. In this study, the hydrothermal method was chosen for the high purity and homogeneity of the particles and the ability to work at relatively low temperatures. In this work, fabrication of cobalt ferrite nanoparticles and chromium doping effect, as (x = 0,0.2,0.4,0.6,0.8 ), effect of annealing temperature at 800°C on uncoated sample,The effect of polyvinylpyrrolidone coating (PVP) on the structural and magnetic properties of ferrite nanoparticles was investigated. After fabricating the samples, we investigated the structural and magnetic properties of the nanoparticles using analysis such as XRD, FESEM and SQUID. The XRD analysis results of sample coated with different PVP values indicate that the structural phase of the sample after coating has not changed and the crystallite size has decreased with increasing PVP coating. SEM images also show increasing in agglomeration by increasing in PVP content. Magnetic measurements show that as the amount of PVP increases, the saturation magnetization of the sample decreases, mainly due to the non-magnetic PVP polymer and the decrease in effective mass. Analysis of the XRD results of chromium-doped samples shows a relatively regular increasing trend in lattice parameter changes. This order is attributed to the distribution of cations at the sites of cobalt-chrom spinel structure. The FESEM results show that by chromium dopping the particle shape changes from spherical to octahedral and the particle size increases. The results of the SQUID analysis of the samples show a decreasing trend in the saturation magnetization behavior and an increase in the coercivity. Saturation magnetization and coercivity decrease with increasing temperature of the SQUID analysis in pure cobalt ferrite samples. It also decreases the coercivity field by annealing the ample.