One sub-type of collocations which is under-researched is binomials. The purposes of this study were to investigate Thai EFL students' knowledge of English binomials, determine the syntactic structure of the internal elements of binomials reported as most or least known by them, and test if the students' knowledge of binomials was significantly different when taking account of their years of study. The sample was 130 first - sixth year students enrolled in four different faculties at a university in northeastern Thailand, and classified as intermediate EFL learners for the purpose of this study through the online Oxford Placement Test. An acceptability judgment test of English binomials was used to collect the data. The results revealed that, on the whole, the participants had a low level of knowledge of English binomials; there was no significant difference in their knowledge regarding the syntactic structure of binomials (Noun+Noun and Verb+Verb); and the participants were not significantly different in their knowledge in terms of their years of study. The results pertaining to the participants' low level of knowledge of binomials were discussed in relation to lack of exposure to English and effective pedagogy of English idioms.