A complete solid solution Ca1-xNa2xTi4(PO4)(6) was prepared between CaTi4(PO4)(6) and Na2Ti4(PO4)(6) belonging to the NASICON structural family. The space group evolves from R (3) over bar for x less than or equal to 0.5, to R (3) over bar c for x > 0.5. For each composition, conductivity values obey the Arrhenius law. From the two end members, cationic substitution improves the conductivity which reaches a maximum for x similar or equal to 0.5. The structure of CaTi4(PO4)(6) was refined in the R (3) over bar space group applying the Rietveld method to the X-ray powder spectra. The Ca2+ cations and vacancies are ordered along the hexagonal c direction. A correlation is proposed between conductivity results and structural features.