Pure Fe3O4 NPs and Oleylamin (OAm) capped MnxFe1-xFe2O4 (MnxFe1-xFe2O4@OAm) (0.2 <= x <= 1.0) nanocomposites (NCs) were synthesized by the polyol route. Lattice parameter increases with increasing Mn2+ concentration, due to the respective larger ionic radius of Mn2+ ion compared with the Fe2+ ion. The VSM analyses revealed superparamagnetic characteristics of all samples. The extrapolated specific saturation magnetization (sigma(s)) values decreased from maximum 50.74 emu/g to minimum 15.34 emu/g by increasing Mn content. The particle size dependent Langevin function was applied to determine the magnetic particle dimensions (D-mag) between 9.10 nm and 21.50 nm. The observed magnetic moments of NPs and NCs are in range of (0.64-2.10) mu(B) and significantly less than 4 mu(B) of bulk Fe3O4. Magnetic anisotropy was determined as uniaxial and calculated effective anisotropy constants (K-eff) are between 32.14 x 10(4) Erg/g and 8.71 x 10(4) Erg/g. The size dependent saturation magnetization suggests the existence of a magnetically dead layers around the magnetic cores for NCs between 0.72 nm and 1.29 nm. From Fe-57 Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Mn2+ substitution have been determined. Although, the Mossbauer spectra for the sample x = 0.2 is composed of ferromagnetic sextets, paramagnetic doublet is also formed for other samples. The percent diffuse reflectance spectroscopy (DR %) and Kubelka-Munk theory were used to specify the optical properties. The estimated optical band gap (E-g) values from Tauc plots are between 1.50 eV and 2.05 eV. Increasing Mn content in NCs increased the band gap at different magnitudes. (C) 2016 Elsevier B.V. All rights reserved.