Imaging-guided photodynamic therapy (PDT) has been regarded as a promising strategy for precise cancer treatment. Because of their excellent modifiability and drug-loading capacity, nanoparticles have played an important role in PDT. Nonetheless, when traditional photosensitizers are made into nanoparticles, both their fluorescence and reactive oxygen species generation efficacy decrease due to a phenomenon known as aggregation-caused quenching. Fortunately, in recent years, several kinds of organic dyes with "abnormal" properties (termed aggregation-induced emission, AIE) were developed. With enhanced fluorescence emission in the nanoaggregation state, the traditional obstacles mentioned above may be overcome by AIE luminogens. Herein, we provide a better combination of photosensitizers and nanoparticles, namely, dual-function AIE nanoparticles capable of producing reactive oxygen species, to implement targeted and imaging-guided in vivo PDT. Good contrast of in vivo imaging and obvious therapeutic efficacy were observed at a low dose of AIE nanoparticles and low irradiance of light, thus resulting in negligible side effects. Our work shows that AIE nanoparticles may play a promising role in imaging-guided clinical PDT for cancer in the near future.