Immobilization of photocatalytic TiO₂ nanoparticles inside PDMS‐based microreactors was successfully attempted by sequential mussel‐inspired surface engineering of microchannels by using CA‐PVP and commercially available TiO₂ nanoparticles, respectively. TiO₂‐immobilized microreactors accomplished continuous photocatalytic degradation of MB for up to 30 days without releasing TiO₂ nanoparticles from the surface of the microchannels, confirming the robustness of TiO₂‐immobilization in photocatalysis media. Regeneration of microreactors with diminished photocatalytic activities was also possible with simple strong acid treatment, enabling efficient cleaning of used microreactors.