Web-based learning has become an important component of education. Higher education institutions in Thailand have become increasingly aware of the widespread use and effectiveness of web-based learning systems. However, the adoption of such learning systems is growing at a slow pace in Thailand. The purpose of this study was to test the Unified Theory of Acceptance and Use of Technology (UTAUT), that performance expectancy, effort expectancy, social influence, and facilitating conditions have a positive effect on usage intention and adoption of web-based learning systems by instructors, in the Departments of Education at the Rajabhat Universities, Thailand; and to test whether experience of use, age, and gender have moderating effects in the adoption of web-based learning systems there. The research design used in this study was a cross-sectional survey design. Data were collected by means of a self-administered paper questionnaire. The study was conducted among the instructors in the departments of education at the Rajabhat Universities in Thailand. A total of 725 surveys were sent out, 454 questionnaires were returned by the respondents, and 14 were eliminated as outliers; thus, the final data set for the study was 440 samples. The two-step approach of SEM was used to test the model and the study's hypotheses; first, the measurement model was measured to examine the validity and reliability of the data; next, the structural model was measured to test the hypotheses of the study and the fitness of the data to the model. The results of this study revealed several factors that can affect instructors’ adoption of a web-based learning system and which can enhance the web-based learning performance of instructors in the Rajabhat Universities and throughout higher education in Thailand.