Completing the Vietnamese criminal procedure law to enhance and better protect human rights, especially to meet international requirements on ensuring the rights of accused persons under 18 years old (referred to as juveniles), is essential for Vietnamese criminal procedure law. The article analyzes the advantages of the legal provisions on proving the age of the accused as a person under 18 years old, thereby pointing out the shortcomings of this regulation to complete proving the age of the accused under 18 years old in the 2015 Criminal Procedure Code (amended and supplemented in 2021), the completion of the above provisions will contribute to ensuring the rights and interests of this particular group of subjects. To complete this article, we have used the main research methods: documentation data collection, writing law analysis, and comparison. These methods will help us clarify the topic’s fundamental issues, such as advantages, inadequacies and solutions of the regulations on proving the age of the accused person under 18 in Vietnamese criminal proceedings.