The aim of this study was to determine the effects of problem-based active learning in science education on students’ academic achievement and concept learning. In the study, both quantitative and qualitative research methods were utilized. Quantitative data were obtained via the pre/post-test, treatment-control groups test model. Qualitative data were obtained via document analysis. The research study was conducted on 50, 7th grade students in 2004-2005 school year, in a public school in Istanbul. The treatment process took 30 class hours in total. In the research, three measurement instruments were used: an achievement test, open-ended questions, and an attitude scale for science education. The reliability coefficient of the achievement test was calculated to be KR20=0.78. Cronbach α value of the attitude scale was 0.89. While the subject matters were taught on the basis of problem-based active learning in the treatment group, traditional teaching methods were employed in the control group. In the face of the data collected and the evaluations made in the research, it was determined that the implementation of problem-based active learning model had positively affected students’ academic achievement and their attitudes towards the science course. It was also found that the application of problem-based active learning model affects students’ conceptual development positively and keeps their misconceptions at the lowest level.