The nanoparticles of Bi2Fe4-xMnO9 (0.0 <= x <= 1.0) were synthesized using the reverse chemical co-precipitation method. The structural and microstructural studies of the synthesized powders were investigated by the X-ray diffractometery (XRD), Fourier-transformed infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectrometer (XPS). The magnetic properties of nanoparticles were measured by a Vibrating Sample Magnetometer (VSM). The dielectric properties of the sintered samples were tested by the inductance-capacitance-resistance (LCR) meter equipment. The structural studies confirm the formation of the single phase of bismuth ferrite without impurities in all compositions. Microstructural observations showed that no significant changes occur in the size and shape of particles by increasing the manganese content. The produced nanoparticles are angular and pseudo-cubic-shaped and the average particle size in each sample is about 130 nm. The magnetic measurement revealed that as the Mn content increases, the coercivity increases noticeably and the saturation magnetization decreases slightly. Also, the dielectric constant was enhanced due to the Mn addition.