Hydrogels, defined as polymer networks with a high water content and insoluble in water, have emerged as pivotal materials in biomedical research due to their resemblance to the natural extracellular matrix. The aim of this study is to develop an injectable, thermoresponsive, and biodegradable hydrogel. The hydrogel (PSI-t) was derived from poly (aspartic acid) (PSI) by grafting hydrophobic dodecylamine (DA) and hydrophilic ethanolamine (EA) groups onto its backbone. PSI-t was found to exhibit a unique sol state at room temperature, which facilitates facile injection, and undergoes rapid gelation at physiological temperatures, highlighting its potential as an injectable thermosensitive hydrogel for targeted drug delivery. In vitro tests confirmed the biocompatibility of the thermosensitive hydrogel, and sustained drug release studies using the model drug, acetaminophen (AP), underscored the efficacy of the hydrogel as a controlled release vehicle. Furthermore, the hydrogel was found to be easily eliminated through bio-hydrolysis, thus enabling prolonged drug effects while mitigating any potential toxicity. These findings suggest that PSI-t is a promising candidate for an innovative and injectable drug delivery system in biomedical applications.