We examined the relationship between English as a Foreign Language (EFL) teachers' interpersonal behaviour and students' fluency in English in secondary education in China. A total of 160 students from four classes in the southwest part of China were asked to assess their teachers' interpersonal behaviour using the Questionnaire on Teacher Interaction (QTI). This was the first time that the QTI was successfully translated and used (in EFL classrooms) in China. Cronbach's alpha reliability coefficients for the scales were adequate, while confirmatory factor analyses provided support for the theoretical framework behind the questionnaire. Results showed that teacher uncertainty was negatively correlated with student achievement. Furthermore, the degree of teacher cooperation with students was the only significant predictor for student achievement, but its effect disappeared when student background variables were taken into account. Results also indicated a discrepancy between students' perceptions of preferred and actual teacher interpersonal behaviour. The tolerant-authoritative profile was the most common interpersonal style based on Chinese students' perceptions.