Micro-photoreactor is a miniaturized photoreactor that integrates the advantages of microfluidics into a conventional photoreactor. Miniaturized photoreactors for wastewater treatment require relatively small quantities of photocatalyst material (femtolitre to nanolitre) and provide unique features such as high surface to volume ratio, better control of reaction parameters and efficient heat and mass transfer. The thin layer of photocatalyst in the microreactor, allows less photon loss and uniform light distribution, making it suitable for photocatalytic wastewater treatment applications. The focus of this review is the recent advancement in the area of microfluidic reactors for heterogeneous photocatalysis with details of reactor design principles, typical reactor configurations, reactor fabrication protocols, choice of reactor material and effect of process parameters such as flow rate, concentrations, light intensity, channel length on the photocatalytic reaction. We also discuss how the limitations faced by conventional photoreactors are addressed by micro-photoreactors in the context of wastewater treatment. © 2021