Mo-doped manganese ferrites nanoparticles with the general formula MnFe2-xMoxO4 (0≤x≤ 0.1) were prepared by co-precipitation technique using two different methods, depending on the molarity of NaOH and the calcination temperatures. The characterization of the prepared samples was conducted by X-ray powder diffraction (XRD), ultraviolet-visible (UV-Vis) absorption spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy in order to investigate the effect of Mo-doping on the structure, crystalline size, energy gap and functional groups of MnFe2O4 nanoparticles. Vibrating sample magnetometer (VSM) was used to study the magnetic hysteresis of samples A and B. The XRD patterns show the dissociation of MnFe2O4 phase into α-Fe2O3 and Mn2O3 for samples prepared at 4 M NaOH and calcination temperature of 873 K (samples A). Whereas, samples B prepared at 2 M NaOH without calcination process, obtained a single phase of MnFe2O4. The Eg of both samples, A and B, decreases with increase in Mo-doping. FTIR confirms the presence of Fe-O bands corresponding to α-Fe2O3 for samples A, and the metal-O bands corresponding to octahedral and tetrahedral sites in samples B. Magnetic measurements show that samples A are antiferromagnetic whereas ferromagnetic behavior is observed in samples B. The dielectric parameters such as real and imaginary parts of dielectric constant (ɛʹ and ɛʹʹ), dielectric loss (tan δ) and ac conductivity (σac) were investigated as function of frequency (10 KHz to 1MHz) and temperature (298K -773K). Dielectric measurements, for both samples A and B, indicate that the dielectric parameters are strongly dependent on both Mo-concentrations and temperatures. Moreover, samples B show higher values of dielectric parameters than those of samples A.