The Ni1 xMnxO (x = 0.00, 0.02, 0.04 and 0.06) nanoparticles were synthesized by chemical precipitation route followed by calcination at 500 degrees C for 4 h. The prepared samples were characterized by energy dispersive analysis of X-rays (EDAX), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). Rietveld refinement of XRD data confirms the structural phase purity and XRD patterns are well indexed to NaCl like rock salt fcc crystal structure with Fm-3m space group. The particle size of Mn doped samples is found to be less than that of pure NiO sample. However, the particle size increases slightly on increasing the Mn concentration due to surface/grain boundary diffusion. The vibrational properties of the synthesized nanoparticles were investigated by Raman and FT-IR spectroscopy. The results of room temperature magnetization (M-H) and temperature dependent magnetization (M-T) measurements are explained with a core-shell model. The synthesized nanoparticles show weak ferromagnetic and super-paramagnetic like behavior at room temperature. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.