This study aims to identify factors affecting students' achievement in science courses from students and faculty's perspective in the College of Science focusing on the following dimensions: student, course, faculty, English as teaching language, and assessment. The population of study was all students and faculties from College of Science in the academic year (2012/ 2013) from majors of physics, chemistry,biology, and earth science, and they were (2239) male and female students and (101) faculties. In addition to (94) male and female students from College of Education (Science Education). The sample of the study was (593) male and female students from college of science and college of education, and (36) faculties from the four majors mentioned above. The researcher used two surveys, one for faculties and the other was for students, consisting of (42) statements. In addition, the researcher conducted focus group discussion with students and individual interviews with faculty. The validity of instruments were verified by a panel of (22) judges. The reliabilities of the surveys were calculated by using Cronbach- Alpha coefficient of internal consistency, and it was (0.87) for student survey and (0.83) for faculty survey. The results of the study revealed that good teacher is the main factor that affects students' achievement in science courses from students and faculty perspective. In addition, results revealed that there is a significant differences in students perspective of factors affecting their achievement in science courses in favor of females in survey's dimensions, student, course, and faculty, and in favor of student with no majors in assessment dimension, where in the academic year of student variable it was in favor of first and second year students in dimension of student and course . moreover, there were no significant differences in variable of students college or any variable related to faculty. Accordingly, the researcher suggested further studies and recommends to fix factors affecting students' achievement to make good education output in college of science, and other recommendations.