Sintering　characteristics,　phase　evolutions,　microstructures,　and　microwave　dielectric　properties　have　been　investigated　for　BaTi4O9　ceramics　prepared　by　traditional　low　temperature　sintering　using　CuO–TiO2　(CT)　additions　as　aids.　The　sintering　temperature　of　BaTi4O9　ceramics　was　found　to　evidently　reduce　from　1350　°C　to　about　1100　°C　with　a　very　small　amount　of　0.5　wt%　CT　addition.　When　the　CT　addition　increased　to　beyond　0.5　wt%,　however,　it　was　not　expected　to　further　lower　the　sintering　temperature.　Meantime,　the　secondary　phases　of　Ba4Ti13O30,　BaTiO3,　and　TiO2　were　observed　in　these　BaTi4O9-based　ceramics　when　the　CT　content　was　beyond　2　wt%.　With　the　introduction　of　the　CT　addition,　the　permittivity　(ε)　had　little　enhancement,　and　the　temperature　coefficient　of　the　resonant　frequency　(τf)　was　improved　to　near　zero.　The　BaTi4O9　ceramics　with　0.5　wt%　CT　additions,　sintered　at　1100　°C,　exhibited　excellent　microwave　dielectric　properties,　such　as　ε　=　36.9,　Q　×　f　=　23100　GHz,　and　τf　=　2.5　ppm/°C.　In　addition,　the　densification　mechanism　and　variations　of　the　microwave　dielectric　properties　have　also　been　discussed　with　the　crystal　phase　and　microstructure’s　evolution.　©　2023　by　the　authors.