The increasing recognition of the negative impact of knowledge risks on the operations of small and medium-sized enterprises (SMEs) has led to a need for effective methods to evaluate and manage these risks. SMEs often adopt a reactive approach to risk management, which may not be sufficient to address the complex and evolving nature of knowledge risks. This study aims to use the grey-DEMATEL technique to evaluate operational knowledge risks in SMEs, with a focus on identifying the most critical risks and their potential causes and effects. The results revealed 11 operational knowledge risks, and found that outsourcing risks are the most critical among them. Communication risks and improper knowledge application were also found to be significant. Additionally, these risks were successfully categorised into effect risks (including relational risk, espionage, knowledge waste, and continuity risk) and causal risks (including knowledge waste, risks related to knowledge gaps, and the risk of using obsolete or unreliable knowledge). These categories provide a framework for understanding the potential causes and effects of operational knowledge risks and may be useful for designing risk management strategies. To the best of the authors’ knowledge, this is one of the first studies to use the grey-DEMATEL technique to evaluate operational knowledge risks in SMEs.