Iron powders are widely used in powder metallurgy for catalysts and other magnetic fluids producing. It was shown [1, 2] that the oxidation of the iron powder is a complicated mechanism, which occurs through the formation of intermediate products and depends on temperature, the rate of powder heating as well as particle structure. Thus, ultrafine iron powders obtained from technology based on an electrical wire explosion have high reactivity, which is increased with the decreasing particle size of powder. In [3] using thermogravimetric (TG) analysis, the oxidation kinetics of ultrafine metallic iron powders, which were made by the electric explosion of wire, were studied and a three-step reaction scheme consisting of two concurrent and one parallel reaction step was suggested. In this work, the effect of mechanical activation on the oxidation of ultrafine iron powders, obtained by electro-explosion method, was investigated by TG analysis through the simultaneous application of non-linear regression to several measurements run at different heating rates (multivariate non-linear regression). The mechanical activation of powders was performed in air for 15 and 40 min using an AGO-2S planetary ball mill with stainless steel balls and vials. TG curves were obtained in STA 449C Jupiter (Netzsch-Geratebau GmbH, Germany) instrument at 1, 3, 5 and 10 K min-1 heating rates. The Netzsch Proteus software packages were used for data analysis. Phase composition of the initial powders and oxidation products were determined by X-ray structure analysis using ARL X’TRA diffractometer with СuKα radiation. The Powder Cell 2.4 software was used for a full-profile analysis of the X-ray diffraction patterns. XRD analysis showed that a certain amount of FeO phase is formed during mechanical activation of ultrafine iron powders. According to TG analysis, a preliminary mechanical activation of powders leads to increasing in the temperature of oxidation onset and shifts the reaction to higher temperatures. In this case, the oxidation is more simple process and occurs in a single step in compared to non-milled ultrafine iron powders where a complex process with three stages are observed. Using TG curves and Netzsch Thermokinetics software package, the kinetic models with minimal adjustable parameters were selected to quantitatively describe the reaction of mechanically activated iron powders oxidation.