The main purpose of the study was to compare the effectiveness of 5E learning cycle model based instruction and traditionally designed chemistry instruction on 10th grade students' understanding of state of matter and solubility concepts. In this study, 119 tenth grade students from chemistry courses instructed by same teacher from an Anatolian High School in Ankara, Turkey took part. This study included two groups which were randomly assigned as experimental and control groups. During teaching the topic state of matter and solubility concepts, students were taught with instruction based on 5E learning cycle model in experimental group while students in control group were taught with the traditional instruction. The results revealed that 5E learning cycle model caused significantly better acquisition of the scientific conceptions related to state of matter and solubility concepts than traditional instruction. (Contains 1 table.)