This article reports a mixed-methods case study on English language teachers' evaluation of an online assessment course and their language assessment literacy. Our goal was to examine the teachers' perceptions of the contents, activities, and the impact of the course on their professional development. For data collection, we used a questionnaire and a focus group interview. Results indicate that teachers welcomed all course contents, especially for assessing learners with special needs and integrated-skills assessment. Regarding activities, the teachers favored test analysis and construction while seeing statistics as irrelevant to their contexts. In terms of professional development, teachers reported reflection on prior assessments and improvements for future assessments. In conclusion, the online course contributed to teachers' knowledge and skills in language assessment.