Abstract: As a new pollutant of global concern, microplastics are widely found in marine environments. Microfiber is the main type of microplastics. However, there are relatively few studies on the aging behavior of microfibers, the effects of ultraviolet light and mechanical abrasion aging on microfibers are not clear. In this paper, based on the common polymers of microfibers found in the beach, polypropylene (PP), polyethylene terephthalate (PET), and polyethylene (PE) were selected to carry out ultraviolet light and mechanical abrasion aging experiments for a period of 8 weeks. The aging characteristics of the microfibers were analyzed combined with infrared spectroscopy and scanning electron microscopy. The results showed that PP masks could be broken to release small-sized (<0.8 mm) microfibers. PP microfibers were oxidized to generate new functional groups by ultraviolet light, while PET and PE microfibers had no obvious changes in functional groups. The mechanical abrasion aging accelerated the shedding of microfibers, the surface of microfibers showed obvious cracks and the fragmentation getting serious with the increase of aging time. The released number of microfibers generated by coarse sand (6.2 microfibers/mm²) was significantly higher than that of gravel abrasion (3.4 microfibers/mm²) after 8 weeks of mechanical abrasion aging. The results of this experiment can help to make up for the lack of existing research and data on the aging behavior of marine microfibers, provide basic data for the sources and fate, environmental behavior and risk assessment of microfibers.