This　brief　presents　a　selective　laser　melting　(SLM)　3-D　printed　Ku-band　diplexer　using　dual-mode　resonators　with　high　thermal　stability.　The　diplexer　is　designed　using　dual-mode　dimpled　ellipsoid　resonators　which　enables　the　diplexer　mechanically　self-supported　in　fabrication.　Hence,　the　design　has　higher　compatibility　with　the　SLM　printing　process　and　the　design　can　be　extended　to　multiplexers　with　more　channels.　The　excellent　thermal　stability　is　benefited　from　both　the　4J36　invar　alloy　material　with　a　lower　coefficient　of　thermal　expansion　(C.T.E)　as　well　as　the　tailored　SLM　printing　process.　Electrical　and　thermal　performances　of　the　diplexer　are　measured,　showing　that　the　fabricated　diplexer　is　with　average　insertion　losses　of　0.69dB/0.42dB,　return　losses　of　＞14dB,　and　centre　frequency　shifts　of　5.62MHz/3.75MHz　(＜0.04%)　in　the　two　channels　after　copper　plating.　The　measured　frequency　shift　is　less　than　0.5　MHz　over　100　degrees　C　temperature　change,　which　is　equivalent　to　a　C.T.E　of　0.5　ppm.