The　nucleation　stage　plays　a　decisive　role　in　determining　nanocrystal　morphology　and　properties;　hence,　the　ability　to　regulate　nucleation　is　critical　for　achieving　high-level　control.　Herein,　glass　microfluidic　chips　with　S-shaped　mixing　units　are　designed　for　the　synthesis　of　Au@Pt　core/shell　materials.　The　use　of　hydrodynamics　to　tune　the　nucleation　kinetics　is　explored　by　varying　the　number　of　mixing　units.　Dendritic　Au@Pt　core/shell　nanomaterials　are　controllably　synthesized　and　a　formation　mechanism　is　proposed.　As-synthesized　Au@Pt　exhibited　excellent　ethanol　oxidation　activity　under　alkaline　conditions　(8.4　times　that　of　commercial　Pt/C).　This　approach　is　also　successfully　applied　to　the　synthesize　of　Au@Pd　core/shell　nanomaterials,　thus　demonstrating　its　generality.　Glass　microfluidic　chips　with　S-shaped　mixing　units　are　designed　to　synthesize　Au@Pt　core/shell　materials.　By　adjusting　the　number　of　mixing　units,　the　hydrodynamics　is　manipulated　to　modulate　the　nucleation　kinetics,　dendritic　Au@Pt　core/shell　nanomaterials　are　controllably　synthesized.　The　hybrid　efficiency　dictates　the　initial　nucleation　state　and　determines　the　ultimate　morphology　of　the　product.image