Abstract: The aim of this research was to investigate the effectiveness of a CLIL based program in developing oral presentation skills and disciplinary knowledge. The participants of the study were 60 third year English Department students at Damanhour Faculty of Education. The experimental group (N=30) received the CLIL- based program, whereas the control group received the regular instruction. The researcher used the pretest-posttest control group design to examine the effect of the treatment. Data collected from the oral presentation test and the disciplinary knowledge test were analyzed. Findings revealed a significant improvement in oral presentation of the CLIL group compared with the non-CLIL group. Findings also indicated significant gains obtained by the experimental group in disciplinary knowledge. A semi structured interview was conducted at the end of the intervention to explore the students' impressions about using CLIL, its potential effect, and challenges. Based on these findings, it was recommended to use CLIL in teaching scientific topics in English. The findings were compatible with many related studies and also the curricular development occurring in the Egyptian pre-university stage.