The objective of this study with first- and second-year undergraduate Thai English as a Foreign Language (EFL) students (N = 813) was to explore the relationships among English writing performance, writing self-efficacy, and writing anxiety. The students wrote an opinion-essay by hand and completed writing self-efficacy and anxiety questionnaires. Their texts were evaluated by EFL instructors using an analytic rubric. Pearson correlations indicated that there was a positive correlation between writing performance and self-efficacy and a negative correlation between writing performance and anxiety. There was also a negative correlation between self-efficacy and anxiety. Implications are recommended for further pedagogic research that take learners’ variables into an account when examining writing performance.