This study aimed at investigating the impact of Content and Language Integrated Learning (CLIL) on higher education students' vocabulary size, content mastery, attitudes toward learning English language, and their perceptions of this method. The study involved a sample of 58 students from Middle East College in the academic year 2019-2020. The experimental group consisted of 28 students, while the control group consisted of 30 students. The research instruments included a vocabulary size test, a content mastery test, a questionnaire on students' attitudes toward learning English language, a questionnaire on students' perceptions of CLIL, interviews, and observations. The results of this study revealed the following findings: 1. There was no statistically significant difference between the control and the experimental groups' scores in the vocabulary post-test and the delayed-test. However, the vocabulary learning gain of the experimental group was higher than that of the control group, which means that CLIL had a positive impact on students' vocabulary size, but this impact was not statistically significant. 2. There were differences between the control and the experimental groups' scores in the content mastery test in favor of the experimental group. However, they were not statistically significant. 3. The experimental group had a high positive attitude toward learning English language at the first time of administering the attitudes questionnaire. Students' attitudes changed slightly after four weeks as a result of implementing CLIL. However, this change was not statistically significant. 4. The experimental group had a high positive perception of CLIL. Students indicated that CLIL enhanced their learning of both language and content. The majority stated that they enjoyed this experience and wanted to be involved in similar CLIL modules. In light of these findings, the researcher presented some recommendations for practice and further research.