<p>The frequency (<i>f</i>)-dependent dielectric properties of Al³⁺ and Cr³⁺ co-substituted magnesium ferrites, MgAl_<i>x</i>Cr_<i>x</i>Fe_{2−2<i>x</i>}O₄ (<i>x</i> = 0.1, 0.5 and 0.7), high-energy ball milled for 3&#xa0;h and 6&#xa0;h duration have been investigated. The grain size reduction and increase in the agglomeration have been observed with milling. The loss tangent decreases with increasing frequency and the resonance peaks have been observed for almost samples after that sharp fall is observed at higher frequency under the influence of milling. The <i>ε</i>' and <i>ε</i>'' versus <i>f</i> plots for <i>x</i> = 0.7 composition milled for 3&#xa0;h and 6&#xa0;h duration demonstrate broad hump mainly due to collective contributions from n- and p-type charge carriers. Cole–Cole plots show incomplete semi-circles correspond to grains and grain boundaries contributions for all the specimens. Representative Nyquist plot has been modelled using equivalent circuit which contains resistor and Q-factor for grain and grain boundary contribution. This behaviour endorsed the high-energy milling impact on the present specimens. Hence, the prepared system with influence of milling is most suitable for the super capacitor application.</p>