Global warming is one of the important environmental problems whose dangerous effects are increasing gradually. The study reported herein aimed to reveal student teachers' conceptions about global warming and the effect of biology teacher education program on their awareness of this environmental issue. An open-ended questionnaire was used to collect the study's data. Participants were 32 first and 37 fifth year biology student teachers. The results showed that both groups had some confusions and concerns about global warming. All of the student teachers were under the impression that ozone layer depletion was the main cause of global warming and they assumed that greenhouse effect was completely an anthropogenic phenomenon rather than a naturally occurring process. In addition, the pre-service education did not seem to have an important effect on student teachers' awareness of global warming. Discussion of the findings and suggestions for teacher education and future research are included at the end of the paper. (Contains 1 table.)