In this study, it is aimed to determine effects of pre-service elementary school teachers' misconceptions about short circuit and open circuit on their ability to set up simple electric circuits. The sample of the research is composed of 41 teacher candidates studying at Dokuz Eylul University. Open-ended questions and semi-structured interview questions prepared by researchers were used to identify misconceptions about short circuit and open circuits. In order to determine the effect of these misconceptions, the pre-service teachers were observed in the process of establishing simple electric circuits. Findings from the open-ended questions show five different misconceptions about the short circuit, and two about the open circuit. The interviews reveal that these misconceptions are caused by three factors: extreme generalizations, the misleading terminology used in everyday speech, and misconceptions arising from past learning experience. It was also determined that the students who held these misconceptions had difficulties in establishing a simple electric circuit.