The objective of this study was to investigate knowledge about, opinions on and attitudes toward and finally readiness to accept genetically modified organisms (GMO) among Slovenian teachers. On average, they have higher levels of knowledge in classical genetics, and poor levels of knowledge about modern issues in biotechnology, and their attitudes toward GMOs are not extreme. They make decisions based on the acceptability of a particular GMO and not on GMOs in general, following two patterns: genetic modifications (GM) microorganisms and plants are more acceptable than animals, and GMOs are more acceptable if they can not be used directly for consumption and produce something recognized as useful. The relationship among knowledge of, attitudes towards and readiness to accept GMO showed that there is no correlation between knowledge and attitudes, only a weak correlation between knowledge and acceptance, and a solid correlation between attitudes and readiness to accept GMO. The practical implication of our findings is that acceptance of GMOs will not be changed by providing new technical or scientific information to teachers but by changing attitudes. The appropriate strategies and actions for improving university courses in biotechnology and the implication for classroom science activities and future research are discussed.