To　determine　multiple　microRNAs　(miRNAs)　from　cells　simultaneously　is　essential　for　understanding　biological　functions.　Capillary　electrophoresis　(CE)　can　simultaneously　determine　multiple　miRNAs　by　separation.　Nevertheless,　similar　lengths　and　low　concentrations　in　cells　make　miRNAs　hard　to　separate　and　detect.　In　this　study,　CE　with　laser-induced　fluorescence　detection　was　combined　with　catalytic　hairpin　assembly　(CHA)　to　determine　three　miRNAs,　miR-21,　miR-31,　and　miR-122.　The　amplification　products　of　CHA,　which　were　DNA　duplexes,　were　designed　to　have　different　lengths　for　different　miRNAs.　This　allowed　for　easy　separation　of　the　duplexes　of　different　miRNAs　by　CE.　The　indirect　determination　of　miRNAs　was　then　achieved　by　separating　and　detecting　these　duplexes.　A　magnetic　field　was　first　applied　on　the　capillary　sieving　electrophoresis　to　assist　in　the　separation　of　the　duplexes.　Under　the　optimal　conditions,　the　three　duplexes　could　be　completely　separated　within　2.5　min　with　the　detection　limits　of　miRNAs　in　the　range　1.12-4.05　x　10-15　M.　MiR-21　and　miR-31　were　successfully　determined　from　Hela　cells,　while　miR-122　was　determined　from　chicken　livers　by　this　method.　The　recoveries　ranged　from　97.5%　to　118%.　The　developed　method　was　sensitive　and　reliable　for　miRNA　determination.