Abstract: Smart materials, as an important class of next-generation functional materials, possess the capability to perceive external environmental stimuli and respond accordingly, and are expected to play an indispensable role in advanced fields such as flexible electronics, biomedicine, and environmental monitoring. With the increasing global pressure on resources and the escalating problem of plastic pollution, polylactic acid (PLA), a biodegradable polyester derived from biomass resources, has attracted considerable attention and has been widely regarded as a promising material platform for enabling the large-scale application and industrialization of smart materials. In recent years, extensive efforts have been devoted to the functionalization of PLA through strategies such as physical modification, chemical modification, and the construction of nanocomposite systems, which endow PLA-based materials with diverse properties including mechanical, electrical, optical, and chemical responsiveness. These advances have significantly expanded the application potential of PLA-based materials in a variety of sensing technologies. In this review, recent progress in the fabrication strategies of PLA-based smart materials and their applications in different types of sensors is systematically summarized. Furthermore, the underlying mechanisms governing performance regulation and the prospects for practical applications and industrialization are discussed, followed by an outlook on future research directions in this field.