Pedagogical content knowledge (PCK) is one of the most important research topics in science teacher education. The purpose of this study was to investigate the PCK of science teachers with different teaching experiences and examine the effects of teachers' PCK on students' achievement and attitudes toward science. A mixed methods research design was used for the study. Participants were science teachers and their students from two middle schools. Interviews, observation forms, achievement tests, and attitude scales were used as instruments for data collection. Data were collected and analyzed using content analysis, descriptive and inferential statistics. The findings obtained from the quantitative and qualitative data showed some significant differences between teachers' PCKs according to their teaching experience. The results also showed that the PCK of a teacher with the least experience was lower than that of the other two experienced science teachers. The results indicated that experienced teachers who developed PCKs did not significantly impact student achievement and attitudes. Educational implications and recommendations for further studies are also provided.