The development of theranostic agents that offer complete biocompatibility, coupled with enhanced diagnostic and therapeutic performance, is crucial for fluorescence imaging-guided photothermal therapy in anti-tumor applications. However, the fabrication of nanotheranostics meeting the aforementioned requirements is challenged by concerns regarding biosafety and limited control over construction. Herein, we reported a class of fluorescence imaging-guided photothermal theranostic nanomaterials that are composed of amino acid derivatives and clinically used small photoactive indocyanine green molecules. Through manipulation of noncovalent interactions, these binary building blocks can co-assemble into nanoparticles in a tunable manner. Significantly, such construction not only maintained the fluorescence properties of photoactive molecules, but also enhanced their stability to overcome barriers from photodegradation and complex physiological conditions. These collective features integrated their precise anti-tumor applications, including fluorescence imaging diagnosis and photothermal ablation therapy. This study reported a class of nanotheranostics characterized by biocompatibility, adjustable construction, and robust stability, which are beneficial for the clinical translation of fluorescence imaging-guided photothermal therapy against tumors.