Sr3La6 (SiO4)(6) is one of the defect silicate apatites. Eu3+-doped Sr3La6 (SiO4)(6), i.e., Sr-3 (La1-xEux)(6) (SiO4)(6) solid solutions, were synthesized and their luminescent properties were studied. The emission intensity increased with increasing Eu3+ concentration up to x = 0.2 and decreased to x = 0.8. At x = 0.9, it raised again dramatically. In addition, the lattice parameter, a, decreased quickly with increasing Eu3+ concentration between x = 0.8 and x = 1.0. This fact was explained by the change of site occupancies of Eu3+,La3+, and Sr2+ ions and defects on the 4f and 6h sites in Sr-3 (La1-xEux)(6) (SiO4)(6).