Asset misappropriation is a kind of fraud that may cause severe damages to the businesses. The internal control system is expected to provide a reasonable assurance for the management of the businesses in preventing and detecting frauds, including asset misappropriation. The study is conducted to examine the effect of internal control system on asset misappropriation in Vietnamese firms. Based on questionnaires collected from internal auditors, accountants and department managers in Vietnamese firms, the study assess the impact of COSO five internal control components on the popularity of asset misappropriation in the firms. The results show that of the five components, control environment presents the strongest impact, followed by control activities, information and communication in respective order. Determinants with the mildest impact are risk assessment and monitoring of control. Based on the findings, it is important that the management of the firms improve the internal controls to effectively reduce the chance of fraud in their firms.