Owing to its capability to be biosynthetic and biodegradable, polylactic acid (PLA) is considered as the most promising biopolymer among all plastic materials, which will play a crucial role as a potentially environmentally friendly material for a sustainable bioeconomy. However, its long life cycle indicates that it cannot be easily degraded in nature. Therefore, understanding the biodegradation mechanism of PLA is important to reduce impacts of waste plastic, waste disposal and alleviate the energy crisis. With the recent development of molecular biological techniques, some studies have confirmed that specific groups of microorganisms may aid the biodegradation process of PLA. Here, recent advances in the biodegradation of PLA (i.e., microbial and enzymatic degradation) and key factors affecting the degradation efficiency were reviewed. In addition, compared to complete degradation through mineralization, upcycling is also proposed as a more recyclable strategy for disposing the waste plastics.