Polar　liquid　distilled　water,　ethanol　and　nonpolar　liquid　R113　were　used　as　the　testing　fluids,　and　let　them　flow　through　a　rectangular　microtube　which　was　made　of　copper　by　crystal　growth　method　with　the　relative　roughness　of　1.40%,　the　hydraulic　diameter　of　170.37　μm　and　the　aspect　ratio　of　0.66,　the　relation　of　Reynolds　number　and　friction　factors,　the　relation　of　Reynolds　number　and　Poiseuille　number,　and　the　relation　of　Reynolds　number　and　gradient　pressure　were　calculated　from　the　measurement　of　the　inlet　and　outlet　parameters　and　the　fluid　flow　velocities.　The　experimental　results　indicate　that　the　polarity　of　the　testing　fluid　is　negligible　during　the　Reynolds　numbers　range　from　43.17　to　4091.5,　and　it　also　demonstrates　that　the　microtube　with　relative　roughness　of　1.4%　almost　does　not　influence　the　frictional　characteristics　in　the　laminar　region;　when　the　Reynolds　number　is　below　1600-1800,　the　experimental　data　for　frictional　factors　of　all　the　testing　fluids　flow　agrees　well　with　the　theoretical　correlation　presented,　when　the　Reynolds　number　is　over　the　range　of　1600-1800,　the　frictional　factors　deviate　from　the　theoretical　correlations,　so　the　transition　to　turbulent　flow　is　validated.　©　2009　Chin.　Soc.　for　Elec.　Eng.