Integrated theranostic nanoplatforms with biomarker recognition and photothermal- and photodynamic (PTT/PDT) therapy is in high demand but remains challenging. Herein, a "sense-and-treat" nanoplatform based on semiconducting polymer nanoparticles (SPNs) for ratiometric bioimaging of phospholipase D (PLD) activity and PTT/PDT combined therapy was proposed. Semiconducting polymer nanoparticles (PSBTBT NPs) serve not only as photothermal agents but also as fluorescent quenchers of Rhodamine B (Rhod B) through a PLD-cleavable linker. Chlorin e6 (Ce6) was used as a photodynamic agent and fluorescence reference. The obtained nanoplatform (PSBTBT-Ce6@Rhod NPs) showed high PDT efficiency and photothermal performance upon single laser irradiation. The PTT/PDT combined therapy achieved more efficient tumor inhibition results as compared with single treatments. In addition, the overexpressed biomarker PLD in tumor tissue will cleave Rhod, leading to the fluorescence recovery of Rhod B and thus allowing the activatable fluorescence imaging of tumor and targeted phototherapy.