This　paper　makes　a　comparison　of　metal　and　dielectric　millimeter-wave　antennas,　which　are　fabricated　by　3D　printing　in　complementary　structure.　These　two　antennas　are　designed　based　on　the　same　tapered　slot　antenna　prototype.　It　was　found　that　the　dielectric　antenna　excites　with　extra　higher　order　modes,　thus　achieves　narrower　main　lobe　and　lower　cross-polarization　level　than　that　of　the　metal　antenna.　The　measured　results　show　that　both　antennas　achieve　wide　impedance　bandwidth　of　28.6%　over　24-32　GHz,　and　have　similar　peak　gains　of　11.3　dBic　and　11.42　dBic　respectively.　Their　fabrication　prototypes　demonstrate　dielectric　antenna　has　a　43%　reduction　in　volume　and　a　90%　reduction　in　weight,　but　might　suffer　from　the　degraded　radiating　performance　due　to　the　fabrication　error.　©　2020　IEEE.