“One-for-all” multifunctional theranostic agents are highly demanded in biomedical fields. However, their design and fabrication still face enormous challenges. Herein, we strategically design and fabricate 1,2-dilauroyl-sn-glycero-3-phosphocholine-modified (DLPC-modified) bismuth nanoparticles (denoted as Bi@DLPC NPs) with desirable size of 47 ± 3 nm as a theranostic agent for photoacoustic (PA) and X-ray computed tomography (CT) imaging guided photothermal therapy (PTT) in response to near-infrared (NIR) laser irradiation. Bi@DLPC NPs possess the excellent photothermal conversion efficiency of 35% and PA/CT imaging properties, which are attributed to the strong NIR absorption and high atomic number (83) of bismuth element. Moreover, it is demonstrated that Bi@DLPC NPs are effectively accumulated in the tumor region because of the enhanced permeability and retention (EPR) effect. With the PTT, the growth of cancer cells (MDA-MB-231 cells) can be remarkably ablated in vitro and in vivo; meanwhile no obvious damage and noticeable toxicity are detected to major organs. The antitumor mechanism of Bi@DLPC NPs is attributable to the mitochondrial dysfunction and change of cell membrane permeability of MDA-MB-231 cells caused by photothermal effects upon laser irradiation. On the basis of their high stability and excellent biocompatibility, Bi@DLPC NPs have great potential for the treatment of various types of tumors.