In　this　study,　polar　liquid　distilled　water,　ethanol　and　nonpolar　liquid　R113　were　used　as　testing　fluid,　and　let　them　flow　through　rectangular　micrtubes　which　were　made　of　copper　by　crystal　growth　method　with　hydraulic　diameters　of　231.91　μm,　250.88　μm,　297.14　μm　and　210.89　μm　and　the　aspect　ratio　of　0.90,　0.70,　0.90　and　0.42,　the　relative　roughness　of　the　microtubes　were　estimated　to　be　1.47%,　1.59%,　1.48%　and　1.45%,　respectively.　The　pressure　drop　between　the　inlet　and　the　outlet　of　the　microtube　as　well　as　mass　flow　rates　were　measured　and　friction　factors　were　calculated　for　different　Reynolds　numbers.　The　experimental　results　indicate　that　the　polarity　of　the　testing　fluid　is　found　to　be　negligible　to　the　frictional　characteristics,　and　meanwhile　it　also　demonstrates　that　the　microtubes　with　the　relative　roughness　below　2%　does　not　influence　the　frictional　characteristics　in　flow　conditions.　When　the　Reynolds　number　is　under　1600,　the　experimental　data　for　frictional　factors　of　all　the　testing　fluids　flow　agree　well　with　the　theoretical　correlation　presented,　when　the　Reynolds　number　is　over　the　range　of　1600-1700,　the　frictional　factors　of　the　microtube　with　the　smallest　aspect　ratio　deviate　from　the　theoretical　correlations　obviously.