BaMg2Fe10O19 hexaferrite particles were synthesized by using a Stearic acid gel method. The prepared Ba-Mg hexaferrite particles were calcinated at Microwave frequency (2.45 GHz, power 900W, 5 min.) as well as at 650°C, 750°C, 850°C and 950°C. Decomposition behavior and the phase associated therein are investigated by means of thermal analysis (DTA, TGA, DSC) and XRD, respectively. The X-ray diffractograms of prepared samples calcinated at 650°C, 750°C, 850°C and 950°C show the presence of M and α- Fe2O3 Phases, whereas the sample heated in a microwave oven shows only single M-phase. Surface morphology of nonporous particles has been examined by using SEM. The samples prepared by conventional heat treatment produces agglomerated clusters of various size particles whereas, the sample heated in a microwave oven shows separate particles with size ranging from 80-240nm. There is significant change in crystallite size of the resultant Ba-Mg hexaferrite particles prepared at microwave frequency. It was observed that heat treatment condition plays a very crucial role in controlling morphology of prepared Ba-Mg hexaferrite particles. Room temperature magnetic measurements were carried out using VSM. Magnetic study reveals that prepared BaMg2Fe10O19 particles possess single magnetic domains.