In this study, the effects of boron (B) doping into MnO delta were examined on structural and magnetic properties. The B-doped MnO delta MNPs were synthesized by polyol method at various B concentration changed from 0 to 15% by 5% steps. Majority MnO and a very weak Mn3O4 crystal diffraction were detected from x-ray diffraction experiments in undoped sample. In contrast to undoped sample, MnO peaks are disappeared and Mn3O4 becomes majority phase when B is doped into the main matrix, as well as observing new crystal orientation called B2Mn3O6. The crystallite size of Mn3O4 phase in undoped sample was calculated to be 62.4 nm. This value nonlinearly decreased to 33.3 nm by amount of B. From scanning electron microscopy images, the particle sizes of the synthesized nanoparticles were determined to be 5.01, 6.77, 6.23 and 7.51 nm for x = 0.0, 5.0, 10.0 and 15.0% in B-x:MnO delta, respectively. The magnetic hysteresis curves indicated that all samples exhibited ferromagnetic (paramagnetic) behavior at 5 K (room temperature). Interestingly, we observed a giant increment in the saturation magnetization (Ms) with boron content. The blocking temperature values obtained from M-T graphs were found to be 24.39, 42.03, 42.14 and 41.91 K for x = 0.0, 5.0, 10.0 and 15.0% in B-x:MnO delta, respectively. (c) 2020 Elsevier B.V. All rights reserved.