The subject of psychological and sociocultural factors influencing English language learning has attracted a great deal of pedagogy researchers' attention. The purpose of this experimental research was to investigate Thai EFL students' silence in the classroom during the pre-and-post implementation of the communicative language teaching approach in an English-medium instruction program in a Thai university context, and to explore the underlying reasons behind this phenomenon. A purposive sampling technique was used to recruit 53 first-year students at an autonomous public university where English is employed as a medium of instruction. A mixed-methods approach to the collection and analysis of data was employed. The findings suggest that the level of silence shown by the students in the classroom environment after the communicative language teaching (CLT) approach had been implemented, was lower than the level of silence experienced in the class prior to the CLT approach being implemented. The significant reasons regarding the students, the teacher, and the Thai cultural concept behind this decrease in students' silence, and the pedagogical implications of that result, are discussed.