Four compositions of spinel NixBa1-xFe2O4 of x =0, 0.05, 0.01, and 0.15 were prepared by the auto-combustion route. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) analyses were utilized to determine the structural properties. All samples showed a cubic spinel structure with a noticeable FTIR tetrahedral band blue shift as the molar ratio x was increased. The crystallite size and particle size have the same behavior as x changed from 0 to 0.15. Spherical nanoparticles aggregated into large clusters were found throughout the samples. Magnetic properties, displayed a drop in magnetization saturation as x increased to its max value. A saturation magnetization (Ms) of more than 48 emu/g was achieved at x = 0 and x = 0.15 while the coercivity did not change clearly. The fitting by the Langevin equation using Originlab software showed very close values of Ms to those measured by the vibrating sample magnetometer (VSM) test. Magnetic parameters are generally affected by both composition and particle size.