Öz This study firstly aims to find out undesirable behaviors encountered at tertiary level language classrooms in general. The second aim is to designate the ones stemming from language learning process. The other important purpose is to investigate the reasons for the identified behaviors from the perspective of both English language teachers and language learners.  The present study was conducted in the preparatory school at a private university in 2016-2017 academic years. The participants were 40 EFL instructors and 42 preparatory learners. The findings were collected through the checklist and interviews. The relevance of the undesirable behaviors with ELT was measured through the checklist. The interviews conducted with EFL instructors and language learners determined the undesirable behaviors particularly related to language learning process and also their reasons were designated. The data was analyzed qualitatively and quantitatively. The study results reveal that there are significant differences in the perspective of EFL instructors and language learners towards undesirable behaviors especially observed at tertiary level language classrooms. It is also seen that the reasons for the identified behaviors are evaluated from the different points of view by EFL instructors and language learners.