CaCu(3)Ti(4-x)MnxO(12)(x　＜=　0.1)　ceramics　has　been　prepared　via　the　conventional　solid-state　method.　The　Mn　substitution　has　strong　effects　on　the　microstructures　and　dielectric　properties　of　CaCu3Ti4O12　ceramics.　The　grain　becomes　obviously　uniform　and　fine　after　a　very　small　amount　of　Mn　substitution　for　Ti.　The　intergranular　phase　gradually　disappeares.　The　bulk　resistivity　increases　from　10(7)　to　10(9)　Omega　cm.　Dielectric　permittivity　is　abruptly　suppressed　to　10(2),　and　dielectric　loss　is　significantly　reduced　to　10-3　for　x=0.004-0.04.　The　better　microwave　dielectric　properties　are　also　achieved　for　CaCu3Ti4-xMnxO12　(x=0.004)　ceramics　as　follows:　epsilon(r)　=68.1,　Q　x　f=　4030　GHz,　tau(f)　=220　ppm/K.　These　results　suggest　that　a　small　amount　of　Mn　substitutions　for　Ti　is　an　effective　way　to　tune　the　microstructure　and　dielectric　properties　of　CaCu3Ti4O12　ceramics.　(C)　2010　Elsevier　B.V.　All　rights　reserved.