In an increasingly uncertain business environment, knowledge is a critical asset for organizations aiming to secure and sustain competitive advantage. Despite its importance, employees often engage in knowledge hiding, which undermines organizational learning and innovation. This study examines the impact of job insecurity on employees’ knowledge hiding, focusing on the mediating role of organizational cynicism and the moderating role of procedural justice. Drawing on Social Exchange Theory, we developed hypotheses and tested them using hierarchical regression analysis on survey data collected from Korean employees. The results indicate that job insecurity is positively associated with both organizational cynicism and knowledge hiding. Furthermore, organizational cynicism mediates the relationship between job insecurity and knowledge hiding. Interestingly, procedural justice demonstrated a significant moderating effect, though this effect was observed in the opposite direction of theoretical expectations. These findings contribute to a deeper theoretical understanding of how job insecurity shapes knowledge-related behavior and offer practical implications for organizations seeking to reduce knowledge hiding in times of uncertainty.