This paper aimed to study a success story of anti-corruption prevention and reduction in the Republic of Korea, or South Korea, via an integrity assessment (IA) of government agency performances. This study also investigated the relationship between the number of people who used to give someone extra money, valuables, or entertainment (as bribery), and the Integrity Assessment Index (IA), Corruption Perception Index (CPI) of South Korea during 2002 through 2012. The study showed that IA and CPI were correlated in the same direction at a statistically significant level of 90 percent. It suggested that IA improvement will give a better result in CPI of South Korea. In addition, the IA and CPI were negatively related to bribery with a statistically high significance of 95 percent. This indicated that bribery in South Korea dropped significantly when IA and CPI rose. Recently, the Office of the National Anti-Corruption Commission (NACC) of Thailand has developed a new model to assess the performance integrity of government agencies based on the South Korean model, integrated with the transparency assessment of NACC to prevent and tackle corruption in Thailand more effectively.