Aurivillius　Na0.5Bi4.5Ti4O15　and　Bi4Ti3O12　compounds　were　synthesized　via　solid-state　reaction　technique.　X-ray　powder　diffraction　study　confirmed　monophasic　four-layered　Na0.5Bi4.5Ti4O15　and　three-layered　Bi4Ti3O12　ceramics.　Dielectric　relaxation　and　conduction　behaviors　of　Na-contained　Na0.5Bi4.5Ti4O15　ceramics　were　thoroughly　investigated　in　a　large　scale　of　temperature　of　30-650　degrees　C　and　frequency　of　40　Hz-1　MHz.　In　addition,　comparative　studies　of　both　the　compounds　were　discussed.　Impedance　and　modulus　analyses　revealed　a　single　relaxation　behavior　in　Na0.5Bi4.5Ti4O15　compound　which　was　originated　from　the　grain＇s　interior　with　grain　resistance　of　2.189　x　10(5)　omega　and　capacitance　of　4.268　x　10(-10)　F　at　570　degrees　C.　While　in　Bi4Ti3O12　ceramic　the　relaxation　was　due　to　the　contributions　of　grain　and　grain　boundaries.　Alternating　current　(AC)　conductivity　analysis　revealed　the　presence　of　two　different　conduction　regions　in　both　the　compounds.　Activation　energies　for　the　two　different　conduction　mechanisms,　i.e.,　in　low-temperature　region　and　in　high-temperature　region　were　calculated　to　be　similar　to　0.23　and　similar　to　1.27　eV　at　1　kHz　for　Na0.5Bi4.5Ti4O15　compound　and　similar　to　0.43　eV　and　similar　to　0.97　eV　at　1　kHz　for　Bi4Ti3O12　compound,　respectively.　The　present　study　of　dielectric　relaxation　and　conduction　behaviors　would　be　helpful　for　further　investigations　of　Na0.5Bi4.5Ti4O15-related　Aurivillius　compounds.