The aim of this study is to investigate the effect of activities developed based on 5E model on grade 10 students' understanding of general properties of gases. The study was conducted in a high school in Akcaabat province of Trabzon, in 2010-2011 academic years. The study used the quasi-experimental design. 40 grade 10 students in two classes were selected for the study. While one of the classes was randomly assigned as experimental group (13 boys, 7 girls), the other was determined as control group (11 boys, 9 girls). In the study, Concept Achievement Test (CAT) including 16 multiple choice items and 4 open-ended questions was used to collect the data. The test was piloted with 50 students and its Reliability Coefficient was found 0,78. In during the treatment, the control group was taught by traditional approach and the experimental group was taught by using the activities developed based on 5E model of the constructivist approach. The collected data were compared by using the independent sample t test. A statistically significant difference in favor of experimental group was detected. It is essential that teachers should develop their skills for designing constructivist learning envirorunent. With this aim, teachers should be given in-service training.