This article investigates the impact of LMS-based integrated online assessment implementation (LbIOA) on fostering learning motivation and academic performance from tertiary students' experiences and instructors' perspectives. A total of 156 students and seven teachers from the English department at a university in Vietnam participated in the study. The mixed-research methods cooperating with qualitative, quantitative, and quasi-experimental ones were employed. The quantitative results show that learners highly evaluated the significance of LbIOA. Student learning motivation increased when LbIOA was applied, compared with the class without the application of the approach. The LbIOA practice had a positive influence on student learning achievement. Additionally, the qualitative data illustrate that the learners had many difficulties in the implementation of LbIOA, including intrinsic and extrinsic barriers. However, teachers had strong beliefs in the take-up of this online assessment type and recommended particular solutions to address the existing issues. Consequently, improving learning autonomy, frequent assessment practice and creativeness in the teaching approach should be implemented to boost student learning motivation and gain academic achievement as expected. Teachers should change the syllabus appropriately to adapt learning to the innovative assessment approach in an IT-assisted educational environment.