Microplastics are ubiquitous in the environment, including in the ocean, soil, and air. Therefore, there are concerns regarding human exposure. Since it is known that the surface of microplastics in various environments is chemically deteriorated by external factors such as ultraviolet rays and waves, it is essential to evaluate the biological effects of degraded microplastics. In this study, we experimented by accelerating the degradation of polyethylene (PE) using vacuum ultraviolet light and prepared PE samples with different degrees of degradation. Then, we evaluated the effects of undegraded and variously degraded PE on cells using cytotoxicity tests. Based on the cytotoxicity test results, we saw a tendency for increased cytotoxicity with increasing degradation. Therefore, this study substantially links the deterioration of microplastics with their biological effects.