This study aims at investigating the effects of case studies developed by the researchers on Science Teaching students' understanding of "gases, liquids and solids," and their attitudes towards chemistry lessons. The study was conducted on 52 freshmen from the Department of Science Teaching at a university in Turkey. Pre-test and post-test experimental design with control group was used, and students were randomly assigned to experimental and control groups. A Prerequisite Knowledge Test was applied to both groups, and independent sample t-test results showed no significant difference between the groups. A preparatory course was applied on both groups to remedy students' lack of pre-knowledge identified by the test results. After the preparatory course, the same educator taught gases, liquids and solids with case study method to the experimental group and with a traditional teacher-centered approach to a control group. The Achievement Tests results showed that the experimental group significantly had higher scores and fewer misconceptions than the control group, and some misconceptions in the control group were identified for the first time in this study. With regard to Attitude towards Chemistry Lesson Scale results, chemistry education based on case studies significantly enhanced students' positive attitudes towards chemistry lessons