In　this　study,　the　flow　and　heat　transfer　characteristics　of　two　multiport　microchannel　flat　tubes　(MMFT)　which　have　same　boundary　dimensions　26　mm　×　2.5　mm,　but　different　internal　structures　were　studied.　Moreover,　the　enhancement　of　heat　transfer　was　compared　with　the　increase　of　friction　factor　to　assess　comprehensively　the　tube　applicability　for　heat　exchanger.　For　the　tube　with　fin　structure,　the　height　of　fin　is　279　μm,　and　the　ratio　of　fin　height　to　hydraulic　diameter　is　15%.　The　experiment　used　water　as　working　fluid　is　performed　with　Reynolds　number　ranging　from　140　to　5900.　The　results　show　that　the　experimental　data　of　friction　factor　and　Nusselt　number　for　smooth　tube　are　in　reasonable　agreement　with　the　conventional　correlations.　And　the　laminar-turbulent　transition　occurs　at　Re=1700,　an　accepted　value　for　macrochannel.　Meanwhile,　laminar-turbulent　transition　of　tube　with　fin　structure　occurs　at　Re=1100,　earlier　to　the　value　for　macrochannels.　Compared　with　smooth　tube,　the　significant　heat　transfer　enhancement　by　using　fin　structure　tube　was　obtained,　while　the　friction　factor　values　are　also　lager　than　that　of　smooth　tube.　The　maximum　heat　transfer　enhancement　is　481%　at　Re=5182　with　penalty　of　friction　factor　increase　of　140%.　A　performance　evaluation　criterion　(PEC)　based　on　same　pumping　power　consumption　for　tubes　with　and　without　fin　structure　was　defined　and　calculated　to　evaluate　the　practical　use.　The　maximum　value　of　PEC　is　about　4.2,　which　is　a　good　value　compared　with　that　of　other　researches.