The purpose of this study was to investigate the effects of science toy making activities on the scientific interest and the conceptual understanding of elementary school students. In this study, science toy making activities were applied to an experimental group and traditional learning activities were applied to the control group. The science toy making activities comprised thirteen steps and were administered during class. In the scientific interest test, there was a statistically significant difference between the score of the experimental group and that of the control group. In particular, post-test scores were higher than pre-test scores in the experimental group, while they were lower than this in the control group. It appeared that students had positive thoughts about science toy making activities. These science toy making activities had positive effects on the conceptual understanding of the experimental group students. The post-test scores of the experimental group were higher than that of the control group in all domain concepts. From these results, it can be deduced that the science toy making activities were more effective than traditional teaming activities. They were an effective teaching technique which enhanced the scientific interests and the conceptual understanding of the students in question.