It has long been well understood and accepted that the prosecution system of Thailand follows the opportunity principleé, where decision not to prosecute could be reasonably made even though the public prosecutor believes that the accused committed the offense in question. Over the years, the Thai legal framework and practice on making decision not to prosecute due to public interest considerations has been evolved in such a way that promising enough in substantive term. As seen from the latest development few years ago, rules governing the Thai prosecutors on this matter has become far better elaborated than before. Nevertheless, the criteria for making such decision based on public interest under the Thai system has not been crystal clear. Since the English law and Crown Prosecution Service guideline on the same topic was looked up to as a good practice when drafting the existing rules of the Office of the Attorney General, and since the prosecution systems of England and Thailand are quite similar in that the prosecutors in both countries have limited roles in the investigation process, there is therefore a good reason to have a comparative insight in both systems for a possible further betterment of the Thai system.