This study presents a comprehensive investigation into the impact of substituting rare earth elements on the magnetic properties of strontium hexaferrite. The samples, synthesized by the sol-gel Pechini method, followed the formula Sr1-xRexFe12O19 with Re = Gd, Sm, Nd, Pr, and La, for 0.025 ≤ x ≤ 0.100. The findings revealed that Re substitution promotes a considerable increment of the coercive field. However, the magnetic yield dropped with increasing the Re content. Therefore, the higher coercivity field, largest magnetization and maximum energy product (BHmax) were reached for samples with x = 0.025. This tendency was consistent across all rare earth-substituted samples although the hexaferrite substituted with samarium and praseodymium showed the strongest hard-magnetic properties. This behavior has been attributed to a reduction of the interaction field due to the emergence of a monodomain structure, and to the limited solubility of rare earth elements within the structure of strontium hexaferrite.