The processes of phase formation in the La₂O₃-Ho ₂O₃-SrO-Al₂O₃ system are investigated in the temperature range 1200-1500°C. The structural characteristics of the compounds described in the studied system are presented. It is established that the formation of (La_1-x Ho_x) ₂SrAl₂O₇ solid solutions proceeds through the formation of LaAlO₃, LaSrAlO₄, SrAl₂O ₄, and SrHo₂O₄ compounds. An increase in the holmium content and the temperature leads to a crossover from the mechanism in which the interaction of LaAlO₃ and LaSrAlO₄ is a limiting stage to the mechanism in which the decisive role is played by the interactions of SrAl₂O₄ with Ho₂O₃ and SrHo ₂O₄ with Al₂O₃.