A method for on-demand droplet coalescence and mixing is realized using laser-induced cavitation bubbles. Water droplets are formed using a microchannel with the coupled T-junction structure. Laser-induced cavitation bubbles are generated inside water droplets to deform the droplets, which break up the continuous phase between the droplets and trigger the fusion process. The diffusion dominated mixing process after the fusion is observed. For two 0.11 pl droplets, they have been mixed in 800 μs to a high mixing quality.