Porphyrin and its derivatives with macrocyclic aromatic conjugation system were excellent organic semiconductor materials and ideal building blocks based on the unique planar, rigid molecular geometry. Molecular self-assembly is a powerful method to the synthesis of nanostructured materials with fine-tuning of the morphology and size. Through designing molecules and supramolecular entities, desired structure and function can be achieved. Here, we report a general microemulsion-based approach to the synthesis of a wide variety of porphyrin nanocrystals with controlled size and morphologies by using different porphyrin as building blocks. This method is based on a designed oil-in-water (O/W) normal microemulsion system. The porphyrin molecules are gathered, assembled, and fixed together spontaneously by the hydrophobic Vander Waals and π-π interaction during controlled evaporation of low boiling point oil solvent in the restricted, micrometer 3-D space provided by microemulsion droplets. The size, shape, component and surface charge of the porphyrin nanocrystals can be controlled by designed experiment parameters. This bottom-up assembly approach opens the way to constructing different monodispersed porphyrin nanocrystals by using oil-soluble porphyrin as building blocks, which may serve as larger building blocks for constructing integrated macroscopic architectures or devices for the fundamental study and practical applications of nanoscience and nanotechnology.