This research investigates how a supportive relationship between teacher behaviour and lexical competence in the English language classroom can improve the learning process. Having a good relationship with students can offer students chances to be motivated and feel engaged in the learning process. The theory behind this study reiterates the predictions that successful teacher-student interaction in the classroom is essential to students' educational and social development and that teachers' understanding of their behaviour is therefore of supreme importance. Lexical competence is the ability to practice a dictionary and how they know the grammar and vocabulary items. For the teachers in teaching, the English language can be improved by using different teaching techniques. Lexical competence and teacher behaviour includes the various aspects that deal with communicating approach with the students. These concepts also help the teacher in acquiring knowledge about how to use vocabulary and presentation skills. The study was conducted to investigate the relationship between teacher behaviour and lexical competence in the English language classroom among secondary level teachers. A standardised scale on teacher behaviour was adapted by the investigator. A lexical competence inventory is developed by the investigator. Suitable objectives were framed, and the null hypotheses was set to test the objectives. A normative survey method was adopted, and a total of 1046 teachers were selected randomly from secondary schools in six districts of Tamil Nadu. The collected data were statistically analysed by using a simple correlation technique and multiple regression analysis. The study revealed a significant positive correlation between the lexical competence and teacher behaviour of secondary level language teachers. Results also showed a significant prediction by the teacher behaviour on lexical competence.