Recent research has demonstrated that ternary aluminum-boron-iodine (Al-B-I2) materials prepared by mechanical milling are effective in generating biocidal combustion products. Such reactive materials are of interest for the munitions aimed to defeat stockpiles of biological weapons. In this research, ternary Mg∙B∙I2 composites were synthesized using two-stage milling. The first stage consisted of a binary B∙I2 powder prepared by mechanical milling, followed by addition of magnesium for iodine stabilization. Specific compositions for each ternary material were varied. Stability of the samples was assessed by their heating in argon at a constant rate using Thermo Gravimetric Analysis (TGA) and observing weight loss. Oxidation of the prepared powders was also studied by TGA. Ternary Mg∙B∙I2 composite powders prepared by two-stage milling were more stable than any of the previously prepared iodine-bearing materials with the same concentration of iodine (20 wt %). Particle size distributions were measured using low-angle laser light scattering. Powders were ignited using in an air-acetylene flame and in a constant volume explosion apparatus. Particle burn times and temperatures were measured optically. Substantially longer burn times and lower temperatures were observed for the prepared materials compared to the reference pure Mg powder.