Electromagnetic (EM) wave pollution is harmful to human health and environment, thus it is absolutely important to develop new electromagnetic wave absorbing materials. MAX phases have been attracted more attention as a potential candidate for electromagnetic wave absorbing materials due to their high conductivity and nanolaminated structure. Herein, two new magnetic MAX phases with multiprincipal elements ((Ti_1/3Nb_1/3Ta_1/3)₂FeC and (Ti_0.2V_0.2Nb_0.2Ta_0.2Zr_0.2)₂FeC) in which Fe atoms replace Al atoms in the A sites are successfully synthesized by an isomorphous replacement reaction of multiprincipal (Ti_1/3Nb_1/3Ta_1/3)₂AlC and (Ti_0.2V_0.2Nb_0.2Ta_0.2Zr_0.2)₂AlC MAX phases with Lewis acid salt (FeCl₂). (Ti_1/3Nb_1/3Ta_1/3)₂FeC and (Ti_0.2V_0.2Nb_0.2Ta_0.2Zr_0.2)₂FeC exhibit ferromagnetic behavior, and the Curie temperature (T_c) are 302 and 235 K, respectively. The dual electromagnetic absorption mechanisms that include dielectric and magnetic loss, which is realized in these multiprincipal MAX phases. The minimum reflection loss (RL) of (Ti_1/3Nb_1/3Ta_1/3)₂FeC is −44.4 dB at 6.56 GHz with 3 mm thickness, and the effective bandwidth is 2.48 GHz. Additionally, the electromagnetic wave absorption properties of the magnetic MAX phases indicate that magnetic loss also plays an important role besides dielectric loss. This work shows a promising composition‐design strategy to develop MAX phases with good EM wave absorption performance via simultaneously regulating dielectric and magnetic loss together.