The aim of this research is to investigate the effect of problem-based learning on misconceptions and conceptual understanding regarding simple electric circuits. Participants are 54 pre-service primary school teachers enrolled on the "Basic Science in Elementary School" course at a state university. The research employs a nonequivalent control group model. The activity sheets containing problem-based scenarios prepared by the researcher were used in the experimental group. In the control group, the lecture-based learning supported by problem solving, question-answer, discussion activities and demonstration experiments was used. Data were gathered by three-tier Simple Electric Circuit Diagnostic Test consisting of 12 questions developed by Pesman (2005). The research revealed that problem-based learning is more effective in improving conceptual understanding and overcoming misconceptions than lecture-based learning.