In this work, dual-mode antibacterial conjugated polymer nanoparticles (DMCPNs) combined with photothermal therapy (PTT) and photodynamic therapy (PDT) are designed and explored for efficient killing of ampicillin-resistant Escherichia coli (Ampr E. coli). The DMCPNs are self-assembled into nanoparticles with a size of 50.4 ± 0.6 nm by co-precipitation method using the photothermal agent poly(diketopyrrolopyrrole-thienothiophene) (PDPPTT) and the photosensitizer poly[2-methoxy-5-((2-ethylhexyl)oxy)-p-phenylenevinylene] (MEH-PPV) in the presence of poly(styrene-co-maleic anhydride) which makes nanoparticles disperse well in water via hydrophobic interactions. Thus, DMCPNs simultaneously possess photothermal effect and the ability of sensitizing oxygen in the surrounding to generate reactive oxygen species upon the illumination of light, which could easily damage resistant bacteria. Under combined irradiation of near-infrared light (550 mW cm-2 , 5 min) and white light (65 mW cm-2 , 5 min), DMCPNs with a concentration of 9.6 × 10-4 µm could reach a 93% inhibition rate against Ampr E. coli, which is higher than the efficiency treated by PTT or PDT alone. The dual-mode nanoparticles provide potential for treating pathogenic infections induced by resistant microorganisms in clinic. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.