The objectives of this research are to study about problems of Thailand’s criminal procedure in case of alleged offenders or defendants who are mentally ill as they appear in Code of Criminal Procedure section 14 and Mental Health Act, B.E. 2551, and also searching for the appropriate legal measures which can use to improve Thailand’s criminal procedure to be more complete and making the alleged offenders or defendants get more justice in criminal procedure. According to studies, it has been found that Thailand’s criminal procedure in case of alleged offenders or defendants who are mentally ill is ambiguous and unclear in many aspects. Firstly, there are no provisions about the process of verifying an order to send the alleged offenders or defendants to hospital for controlling and treatment and order to bring them back into prosecution. Secondly, there are no time frames about controlling the alleged offenders or defendants in the hospital. Finally, the right to counsel of the alleged offenders or defendants is unclear. The lacks of clarity in these criminal procedures cause the alleged offenders or defendants will not be protected in criminal procedures as they should be, and may cause unfairness in the cases. For these reasons, this research recommends to amend Code of Criminal Procedure and Mental Health Act, B.E. 2551 by establishing provisions about the process of verifying an order to send the alleged offenders or defendants to hospital, order to continue proceeding and the order to bring them back into prosecution including the opportunity for the defendant to dispute the accuracy of these orders, setting time frames about controlling the alleged offenders or defendants in the hospital, and specifying that all of alleged offenders or defendants who are mentally ill will be required to have a lawyer throughout the litigation process. These legal measures will result in the alleged offenders or defendants who are mentally ill being properly protected in the course of criminal proceedings
