Phototheranostics involving both fluorescence imaging (FLI) and photodynamic therapy (PDT) has been recognized to be potentially powerful for cancer treatment by virtue of various intrinsic advantages. However, the state-of-the-art materials in this area are still far from ideal towards practical applications, owing to their respective and collective drawbacks, such as inefficient imaging quality, inferior reactive oxygen species (ROS) production, the lack of subcellular-targeting capability, and dissatisfactory theranostics delivery. In this contribution, these shortcomings are successfully addressed through the integration of finely engineered photosensitizers having aggregation-induced emission (AIE) features and well tailored nanocarrier system. The yielded AIE NPs simultaneously exhibit broad absorption in visible light region, bright near-infrared fluorescence emission, extremely high ROS generation, as well as tumor lysosomal acidity-activated and nucleus-targeted delivery functions, making them dramatically promising for precise and efficient phototheranostics. Both in vitro and in vivo evaluations show that the presented nanotheranostic system bearing excellent photostability and appreciable biosecurity well performed in FLI-guided photodynamic cancer therapy. This study thus not only extends the applications scope of AIE nanomaterials, but also offers useful insights into constructing a new generation of cancer theranostics.