In this paper, we report our investigation on material structure analysis of (Ba0.7Sr0.3Fe12O19)1-x-(Ba0.7Sr0.3TiO3)x with x = 0.2, x = 0.5 and x = 0.8 composite system prepared by a mechanical alloying process to promote feroic properties. It is shown that the x-ray diffraction patterns of each composition for the composite materials are the same. It consisted of the mixture for the two phases. The average of particle size for each respective phase in the composite materials was found initially increased, up to 18-20 μm after mechanically milled for 40 hours, then start to decreased to a smaller size ~ 8-10 μm after 80 hrs milling time. However, a plot of particle size against the milling time for each composite phase shown a trend of further reduction in the mean particle sizes. In addition, the x-ray traces of dense pellet samples after sintering the milled powders at a temperature of 1100 °C showed broadened diffracted peaks pattern due to fine crystallites in the samples. Results of mean crystallite size determination of respective phases in the composite samples showed the same trend, a decrease with milling time toward values about 10 nm at 80 hrs milling time. Hence, sintering to the milled particles has promoted the formation of nanocrystal containing particles. When compared between the mean particle size and mean crystallite size of respective phase in the composite samples, the mean crystallite size for magnetic phase (B7S3F) was found more than 100 times smaller than the mean particle size of composite particles. However, finer mean crystallite sizes were found in the ferroelectric phase (B7S3T) in which the mean was about 200 times smaller than the mean particle size.