The paper presents an intensive study of a micro-event aiming at the characterization of teacher's discourse from a multimodal communication perspective in a secondary school science classroom dealing with the topic of "water cycle." The research addresses the following questions: (a) What communicative modes are used by the teacher?, (b) what role do the different communicative modes play within teacher's discourse?, and (c) what are the relationships among communicative modes being used by the teacher? Theoretical framework is developed based on three strands: multimodal communication, science teaching and learning as modeling, and social semotics and Halliday's functional grammar. An analytic scheme guiding teachers' discourse analysis is presented and results discussed. Implications for science teacher education are drawn that would contribute to the improvement of science teacher education.