The synthesis of MgO and Mg99%Agl%0 nanopowders was performed by Sol-gel method in gelatin media. The prepared powders were characterized usmg X-ray diffraction analysis (XRD), fourier transform infrared (FT-IR) spectroscopy, UV-Visible spectroscopy and transmission electron microscopy (TEM). Also, antibacterial property of the prepared samples was investigated by spectrophotometric method on Gram-negative Escherichia coli and Gram-positive, Bacillus subtilis. XRD analysis showed the structures of the prepared samples are cubic. The crystallite sizes were determined by size-strain plot (SSP) method. For pure MgO, the average crystallite size was found about 20 nm and for MgO and Ag particles in Mg99%Agl%0 nanocomposite is 23 and 44 nm, respectively. FT-IR specteroscopy confirmed the formation of MgO with vibration mode of Mg-O. TEM image showed the spherical shape of the particles with the average diameter of 21nm. The UV-Vis specteroscopy indicated that the energy band gaps of MgO andMg99%Agl%0 are 4.5 and 5.2eV, respectively.Mg99%Agl%0 and MgO nanocomposite showed high antibacterial activity against E.coli especially in 550pg/ml and 750pg/ml concentration. Mg99%Agl%0 nanocomposite in 250pg/ml had more antibacterial activity comparing to Mgo which most probably could be due to the existence of Ag nanoparticles in Mg99%Agl%0 nanocomposite. Also, it was found out that MgO nanopowders completely inhibit the growth of B. subtilis, in 550pg/ml and 750pg/ml of nanopowders.

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