Photothermal sensing exploits the photothermal effect, characterized by high precision, rapid response, simple construction, and cost-effectiveness, and recently, it has experienced substantial growth in the field of biomedicine. Nanomaterials, with diameters ranging from 100 to 1000 nm, exhibit superior performance compared to conventional materials. Nanomaterials have gained widespread use in photothermal sensing owing to their efficient photothermal conversion and favourable biocompatibility. This article introduces the principles of photothermal sensing technology. Subsequently, it delves into the composition and structure of photothermal sensors and reviews the utilization of these nanomaterials in sensing, encompassing inorganic, organic, and composite photothermal nanomaterials. It also summarizes the latest advancements in temperature measurement tools commonly employed in detection and their progress. Finally, it offers insights into the future development of photothermal sensors leveraging nanomaterials. This article is a valuable reference for researchers synthesizing stable nanomaterials with heightened photothermal conversion efficiencies and devising more efficient and sensitive detection methodologies.