This study investigates the efficacy of alginate oligosaccharides, derived from a novel alginate lyase expressed in E. coli (Pet21a-alginate lyase), in preserving the postharvest quality of litchi (Litchi chinensis Sonn.) fruits. The alginate lyase, characterized by Huang et al. (2013), was employed to produce AOS through enzymatic degradation of alginate. The resulting oligosaccharides were applied to litchi fruits harvested from Guangzhou Zengcheng to evaluate their impact on various quality parameters under controlled storage conditions. The study focused on measuring the effects of alginate oligosaccharide treatment on the fruits' color retention, water loss rate, hardness, and susceptibility to mold infection, under a set relative humidity and temperature. Results demonstrated significant improvements in the treated fruits, with enhanced color retention, reduced water loss, maintained hardness, and lower rates of mold infection compared to untreated controls. These findings suggest that AOS offer a promising natural alternative for extending the shelf life and maintaining the quality of litchi fruits postharvest.