This study aimed at determining outcome of research-based learning instruction for Nursing Care of Persons with Mental Health Problems course performed by undergraduate students in Nursing Science Program. The study employed an action research practice conducted at Boromarajonani Nursing College in Ratchaburi. The samples were 77 students enrolling in the course in the second semester of 2017 academic year. An achievement test for assessing the academic knowledge in the course was used for data collection. Content analysis and descriptive statistics was used for outcome analysis. The findings showed that the students learning with the research-based instruction had higher learning achievement on the course than those learned with the normal instruction.