Advancements in science and technology have created problems for some people who have difficulties adapting to the new environment. Improving problem solving skills of these people is very important for them to so have the ability to cope with new problems. From the education perspective, it is believed that teachers should help students by not only giving them information on how to solve certain problems but also how to assimilate problem solving skills. Teachers should first and foremost have these problem solving skills so that they can help their students. In this context, the aim of the current work is to study pre-service science teachers' problem-solving skills and to determine the effect of science teacher training program on pre-service science teachers' problem solving skills based on their grade levels. 76 freshmen, 81 sophomores, 117 juniors and 69 seniors (that is, 343 pre-service science teachers in total) of the Department of Science Teacher Education in 2012 to 2013 academic year participated in this study. In order to measure their problem solving skills, problem solving inventory (PSI) which was developed by Heppner and Petersen and adapted into Turkish by Sahin, Sahin and Heppner was used. In the data analysis procedure, One-Way ANOVA was used to determine whether there is any statistically significant difference among grades, scores of problem solving skills, and its dimensions. According to the findings, significant differences were found between sophomores and juniors; and also between sophomores and seniors. As for the sub dimensions, there was only found a significant difference according to "impulsive style" and "avoidant style" dimensions among grades. [This study was presented as a research paper at the International Conference on Education in Mathematics, Science and Technology (ICEMST-2014) organized on 15-19 May 2014, Konya, Turkey.]