The aim of this research was to investigate the effect of science course which is based on inquiry based learning approach on seventh grade students' scientific process skill levels. Both quantitative and qualitative data collection methods were used in the study. Considering that both quantitative and qualitative data collection methods were used, the study involved a mixed-method design. The research process was carried out according to the simultaneous transformational mixed research design. The study group consisted of 40 students at seventh grade who were studying in public schools in a district in the western part of Turkey in the 2016- 2017 academic year. The data analysis was carried out with Scientific Process Skills Scale and Semi-Structured Interview Form. The obtained data were analyzed using statistical methods. As a result of the study, it was determined that the scientific process skill levels of the students in the experimental group increased statistically significantly compared to the students in the control group. Additionally, the results obtained in the analysis of qualitative data support the results obtained from the quantitative data.