Many educational institutions have adopted online assessment in recent years. Previous studies on online assessment have often been tied to studies on learning management systems. As such, questions of online assessment acceptance have typically been overshadowed by a focus on the acceptance of learning management systems in general. The focus of the present research on online assessment is relatively rare. This paper describes the validation of an instrument to measure online assessment adoption by lecturers in higher education. A total of 213 participants responded to a 20-item online questionnaire. With the data collected and the model fit, the instrument developed was able to meet the expectations to measure online assessment. The preliminary evidence of the validity of the extended Unified Theory of Acceptance and Use of Technology model, based on its reliability found in the current study, supports the use of the instrument as a technology acceptance framework for online assessment systems.