In this study, the effect of science and research ethics course on preschool teacher candidates' possible plagiarism behaviors was examined. Fifteen teacher candidates were asked to prepare a written assignment (pre-test) before the start of the course. Similarly, a second written assignment (post-test) was taken at the end of the course which took approximately 12 weeks. Both assignments received from teacher candidates were evaluated in two similarity/plagiarism software programs and the similarity rates of each student's homework were calculated as a percentage. The Wilcoxon Signed Ranks Test was used to test whether there was a significant difference between these percentage scores in terms of pre-test and post-test. In addition, teacher candidates' pre-test and post-test assignments were subjected to document analysis in the context of the matches determined by similarity/plagiarism software programs. According to the findings of the study, it was seen that science and research ethics course could have an effect on possible plagiarism behaviors of teacher candidates. The findings of the study were discussed regarding similarity/plagiarism software programs, course period and literature. Suggestions were made to help teacher candidates and to those who are concerned about avoiding unethical practices.