Perovskite type ceramic La_0.8Sr_0.2MnO₃ have interesting properties for use as cathode materials for solid electrolyte fuel cells, SOFC. The aim of this work was to prepare materials perovskite La_0.8Sr_0.2MnO₃ type using solid state reactions upon mechanical activation of the precursor to achieve a total reaction during heat treatment at 1100 ° C for 6 hours, without residual phases that avoid the correct transfer of ions and electrons at the interface electrolyte electrode in the fuel cell, and to prevent the formation of undesirable phases at the interface as La₂Zr₂O₇ due to possible excess La₂O₃ at the cathode [1]. The mechanical activation was carried out with a reactor mechanofusion. The distance between the wall and the blades (gap) and processing time were varied in order to know their behavior (gap: 0.7 mm and 1.1 mm; time: 1 to 3 hours). The study reported that a 0.7 mm gap reached a higher percentage of perovskite phase with a 76% compared to a 1.1 gap reaching only a 8% of the desired phase. Similarly, when 3 hours of  time was used best results were observed reaching a percentage of 26 compared to a 8% pervoskite phase when one hour of treatment was used. The distance between the wall and the blades (gap) and processing time are critical parameters for mechanical activation.