Phototherapy, including photodynamic therapy and photothermal therapy, is an emerging form of non‐invasive treatment. The combination of imaging technology and phototherapy is becoming an attractive development in the treatment of cancer, as it allows for highly effective therapeutic results through image‐guided phototherapy. Porphyrins have attracted significant interest in the treatment and diagnosis of cancer due to their excellent phototherapeutic effects in phototherapy and their remarkable imaging capabilities in fluorescence imaging, magnetic resonance imaging and photoacoustic imaging. However, porphyrins suffer from poor water solubility, low near‐infrared absorption and insufficient tumor accumulation. The development of nanotechnology provides an effective way to improve the bioavailability, phototherapeutic effect and imaging capability of porphyrins. This review highlights the research results of porphyrin‐based small molecule nanoparticles in phototherapy and image‐guided phototherapy in the last decade and discusses the challenges and directions for the development of porphyrin‐based small molecule nanoparticles in phototherapy.