Herein, we report a continuous flow methodology for the facile and high-yielding synthesis of the porphyrin-based self-assembled organic cage, P12L24, along with the serendipitous discovery of a kinetic product, P9L18 cage, which has been characterized by MALDI-TOF MS, NMR, and AFM analysis. A theoretical study suggests a tricapped trigonal prismatic geometry for P9L18. Unlike P12L24, P9L18 is unstable and readily decomposes into monomers and small oligomers. While the batch synthesis produces only the thermodynamic product P12L24, the continuous flow process generates not only the thermodynamic product but also kinetic products, such as P9L18, illustrating the advantages of the continuous flow process for the synthesis of self-assembled cages and the exploration of new non-equilibrium assemblies.