Abstract: The present invention provides an ultrasonic micromixer which is used in fields of bio-MEMS (micro-electro-mechanical-system) and ?-TAS (total analysis system) and radiates ultrasonic waves using a piezoelectric device in a direction perpendicular to a horizontal mixing interface between a plurality of sample fluids flowing in a chamber, so as to accelerate the mixing of the sample fluids, thus producing an evenly mixed sample. The ultrasonic micromixer includes a plurality of independent inlets, and a plurality of guide channels which are coupled to the inlets at different heights. The ultrasonic micromixer further includes the chamber to allow the plurality of sample fluids, discharged from the guide channels, to mix with each other while flowing through the chamber, and an outlet to discharge the mixed sample fluids.