This study examines the practical effectiveness of restructuring which has recently become a pressing issue. It analyzes whether restructuring through workforce reduction enhances firm performance and investigates whether the efforts companies put into restructuring lead to fundamental and efficient corporate downsizing. Using firms listed on the KOSPI from 2012 to 2021, the study first finds a negative relationship between human resource downsizing and firm performance. Second, this study finds a statistically significant negative relationship between regular employees downsizing and firm performance only in samples where the number of non-regular employees has increased. This result suggests that companies replacing regular employees with non-regular employees experience a decrease in firm performance, indicating that simply symbolic restructuring can negatively impact firm performance.By examining the negative aspect of regular-to-non-regular transition in the process of workforce restructuring, this study provides practical implication for the direction of workforce restructuring in companies.