The　characteristic　of　flow　and　heat　transfer　of　Al2O3-H2O　nanofluids　flowing　through　a　micro　heat　sink　with　complex　structure　under　constant　heat　flux　is　investigated　experimentally.　The　volume　fraction　and　Reynolds　number　of　Al2O3-H2O　nanofluids　ranged　from　0.1　vol.%　to　1.0　vol.%　and　100　to　700,　respectively.　Moreover,　the　effects　of　them　on　friction　factor,　Nusselt　number,　and　thermal　resistance　are　also　considered.　The　results　show　that　single　phase　model　underestimates　the　friction　factor　and　Nusselt　number　of　nanofluids　from　the　experiments.　With　increasing　volume　fraction　and　Reynolds　number,　both　Nusselt　number　Nu　and　friction　factor　f　of　nanofluids　increase　while　the　average　temperature　at　the　bottom　and　thermal　resistance　decrease,　as　compared　to　deionized　water.　Moreover,　new　correlations　off　and　Nu　are　presented　based　on　experimental　data　with　the　maximum　deviation　less　than　+/-　5%.　The　performance　evaluation　plot　shows　that　the　higher　slope　of　values,　i.e.,　higher　volume　fraction　of　nanofluids,　gives　better　comprehensive　performance　of　heat　transfer.　The　compound　heat　transfer　enhancement　techniques,　i.e.,　cavities　in　the　micro　heat　sink　and　nanofluids　can　obviously　enhance　heat　transfer.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.