Some results on the mechanochemical synthesis of apatites with simultaneous substitutions of calcium by lanthanum and of phosphate by silicate are presented. The reagents of reaction mixtures are taken such that to synthesize the compounds containing equal concentrations of lanthanum and silicon. The synthesis is performed in an AGO-2 planetary mill. The complete conversion of initial reagents in the synthesis of substituted apatite takes a longer period as compared to the time required for the synthesis of unsubstituted apatite. The mechanochemical synthesis time must be 40 min to synthesize lanthanum-and-silicate substituted apatite with a degree of substitution of <6 mol. When the concentration of substituents is higher than 6 mol, the total conversion of initial reagents occurs after 100 min of mechanical impact.