An organic surfactant/stabilizer plays a critical role in synthesizing small and well-dispersed nanoparticles with large catalytic surface areas. However, a stabilizer typically interferes with the catalytic reaction by forming organic layers on the surface of nanoparticles. Here, we report that the role of a stabilizer can be replaced by the periodic and uniform fluid shear of Taylor vortex flow. Small, well-dispersed PdAg alloy nanoparticles on carbon were synthesized in the continuous Couette-Taylor (CT) reactor in the absence of a stabilizer. The synthesized PdAg nanoparticles (Pd64Ag36/C) showed two times higher mass activity than commercial Pd/C and good stability (retained 33% after 3,600 s) toward the electrochemical ethanol oxidation reaction due to their clean surface and alloy structure.