Solid solutions in bismuth layer structured Bi5Ti3Fe1-xMnxO15 (x = 0-1) system were prepared, and evaluations of crystal structure and electrical properties were performed. Polycrystalline samples were synthesized by the solid-slate reaction technique using component oxides, and their powder X-ray diffraction (XRD) patterns were analyzed by the Rietveld method using the RIETAN program. The Bi5Ti3FeO15 structure was maintained in the region of 0 less than or equal to x less than or equal to 0.4, but a structural change was suggested at x greater than or equal to 0.5. The substitution of Fe3+ site by Mn3+ ion in Bi5Ti3FeO15 was found to shift the Curie temperature T-c toward the low-temperature region and to decrease the dielectric permittivity at T-c in the region of 0 less than or equal to x less than or equal to 0.4. The relationship between atomic displacement of B site ions (Ti4+, Fe3+, Mn3+) and the Curie temperature is discussed.