Purpose: In recent years, scholars have questioned the linear relationship between challenge stressors and positive outcomes. Nevertheless, few studies have examined whether challenge stressors and workplace learning outcomes have an inverse U-shaped relationship. Therefore, this study aims to determine whether challenge stressors have an inverse U-shaped relationship with workplace learning outcomes among young Japanese employees. Design/methodology/approach: Data were collected from 1,257 individuals in two time periods through an internet survey and analyzed using regression analysis. Findings: The findings suggest that challenge stressors have an inverse U-shaped relationship with workplace learning outcomes. Practical implications: The relationship between challenge stressors and workplace learning outcomes is positive until a certain point and becomes negative after a certain point. Hence, when promoting learning outcomes among young employees, supervisors should be careful to avoid subjecting employees to very little or excessive amount of challenge stressors. Originality/value: This study provides evidence supporting the assumption that the relationship between challenge stressors and positive outcomes has an inverted U-shape.