The present study aimed to evaluate whether a chemistry laboratory course called "Laboratory Experiments in Science Education" based on constructivist instruction accompanied with concept mapping enhanced pre-service chemistry teachers' conceptual understanding. Data were collected from five pre-service chemistry teachers at a university in Ankara by means of a concept test and semi-structured interviews. Results showed that pre-service teachers had some alternative conceptions about chemistry topics. Moreover, using constructivist instruction accompanied with concept maps as an instructional tool was effective to promote conceptual understanding. Participants thought that concept maps were useful especially in recognizing the relation between different chemistry concepts.