Photoacoustic imaging (PAI) is a hybrid imaging method based on photoacoustic (PA) effects, which is able to capture the structure, function, and molecular information of biological tissues with high resolution. To date, therapeutic techniques under the guidance of PAI have provided new strategies for accurate diagnosis and precise treatment of tumors. In particular, conjugated polymer nanoparticles have been extensively inspected for PA-based cancer theranostics largely due to their superior optical properties such as tunable spectrum and large absorption coefficient and their good biocompatibility, and abundant functional groups. This mini-review mainly focuses on the recent advances toward the development of novel conjugated polymer nanoparticles for PA-based multimodal imaging and cancer photothermal therapy.