Visible-light photocatalysis is a mild activation mode for small molecules synthesis and enables a wide variety of transformations that are difficult or impossible to reach via thermochemical activation.1,2 However,one of the limitations of photocatalysis and photochemistry in general is the limited scalability due to the absorption of light(Lambert-Beer law).In this work,a convenient numbering-up strategy for the scale-up of gas-liquid photocatalytic reactions was proposed.The numbered-up systems could be rapidly assembled with commercially available constituents.The modular design allows us to systematically scale the photochemistry within 2n parallel capillary microreactors(herein,n = 0,1,2,3).The flow distribution with and without reactions(photocatalytic aerobic oxidation of thiols to disulfides)was excellent,showing a standard deviation less than 10%.The yield of the target disulfide in the numbered-up assemblies was comparable to the results obtained in a single device demonstrating the feasibility of our approach.