Injuries and deaths resulting from driving under the influence of alcohol (DUI) have become a major problem in Thailand. Specifically, the World Health Organisation (WHO) reported that Thailand's road-traffic death rate (per 100,000) was ranked third of 182 countries in 2013. To date, no research has examined whether the 2007 Road Traffic Act (RTA) has had a significant impact on DUI accidents since it was enacted. Accordingly, the purpose of this study is to evaluate the impact of the 2007 RTA on DUI accident rates in Thailand. Using monthly DUI accident figures from 2005 to 2010 obtained from the Police Information and Technology Centre, the results from an interrupted time series design are used to indicate whether the new RTA is more effective than the previous Act in preventing drugand alcohol-related accidents in Thailand. The results supported the effectiveness of the 2007 RTA, but only in Region 10 (Bangkok), Region 1 (Nonthaburi) and Region 3 (Nakhon Ratchasima). However, it is important to highlight that even though the 2007 RTA was statistically significant in only three regions, the number of DUI accidents decreased in all 10 regions. Suggestions for future research are also provided.