Photoacoustic imaging (PAI) has evolved to a stage that high-performance exogeneous contrast agents are urgently needed for imminent biomedical and clinical applications. Given that a material meets the basic criteria of efficient photoacoustic conversion, high biocompatibility, and fast excretion, great effort has been devoted to evaluating various materials for developing advantageous contrast agents to explore the full potentials of PAI. One focus is through modification of the current agents to boost their PA performance; whilst the other focus is to develop novel agents. Antimonene (AM) has emerged as a promising candidate for next generation of electronics among 2D materials due to its outstanding properties. Herein, it is reported that liquid-phase exfoliated antimonene exhibits extraordinary photoacoustic performance, which is not only more advantageous than other 2D materials, such as black phosphorus, graphene oxide, and transition metal dichalcogenides, but also superior to the commonly used PA contrast agents, such as ICG and gold nanorods. An insight analysis reveals that the unique thermal property of AM, including intrinsic low thermal conductivity and the morphology-related high interfacial thermal conductivity, might interpret the high photothermal conversion efficiency, and thus the excellent photoacoustic performance. The prodigious performance allows sensitive monitoring of intracellular events and high-quality in vivo tumor imaging.