The purpose of this study was to investigate the effectiveness of guided inquiry based learning strategy over traditional teaching method in improving grade seven students’ learning about physical and chemical change concepts. The participants N=55 (28 males and 27 females) were seventh grade Sadasa elementary school students in Kemissie town of Amhara regional state, Ethiopia. Quasi-experimental nonequivalent pretest-posttest design was used. Two classes (groups) from the school were randomly selected from four available classes (groups). The experimental and control group was assigned after their pretest was analyzed. The experimental group was taught by guided inquiry based learning strategy while the control group was taught by traditional teaching method. Open ended questions related to physical and chemical changes were administered as pre- and post-tests to students in both groups. Furthermore, structured interview was conducted to students in the experimental group at the end of the study in order to get students’ attitudes about guided inquiry based learning strategy. The pretest and posttest data were analyzed by using independent samples t-test and paired samples t-test. The students’ interview about guided inquiry based learning strategy was transcribed and then analyzed. Independent samples ttest revealed that experimental and control groups were scored almost similar before the intervention. After the interventions, independent samples t-test and paired samples t-test analysis indicated that students in the experimental group scored significantly higher than in control group. Thus, guided inquiry based learning strategy was more effective to improve student’s achievements in physical and chemical changes concepts than traditional teaching method. Thematic analysis indicated that students in the experimental group demonstrated high level of interest and positive attitudes toward the guided inquiry based learning.