Education is a process by which man transmits his experiences, new findings, and values accumulated over the years, in his struggle for survival and development, through generations. Accordingly, one of the aims of education is to strengthen the individual's and societies' problem solving capacity, ability and culture starting from basic education and at all levels in each field (FDRGE, 1994). The general objective of this study is to determine the key factors influencing students' academic achievements measured by CGPA of students. The data for the study were obtained through questionnaire method that covers various factors related to students' academic achievement including educational and socio-demographic backgrounds of pupils and their parents, economic background of parents, lecturers' characteristics and general university facilities. The data collection instrument (that is questionnaire) was prepared in English. Students included in the sample were selected using systematic random sampling technique from those representative departments and batch's. The analysis used multilevel linear regression to analyze the data in order to identify determinants of both school and department variation in students' academic achievements measured by CGPA of students. University entrance Exam result, sex, mother education level, father education level, drug use, number of assessments, and group study status were found to be determinants of academic achievement in the total sample of students. In contrast, sexual partner and teacher education level were not significantly related the academic achievement of students. In conclusion, to increase the success of students and reduce variability of academic achievement both between college/school/institute and departments, there is clear need of promoting group work and put efforts for its effectiveness. In addition, both college/school/institute and departments should give great attention in supporting female students.