This study aimed at determining the effects of using a computer algebra system (CAS) on undergraduate students' spatial visualization skills in a calculus course. This study used an experimental design. The "one group pretest-posttest design" was the research model. The participants were 41 sophomore students (26 female and 15 male) studying at an undergraduate program in the department of mathematics in the west Anatolia region of Turkey. In order to determine students' spatial ability, The Purdue Spatial Visualization Test: Visualization of Rotation (PSVT-R) was used as the pre-test and post-test. This test consists of 30 multiple choice items and it assesses the skills of mental rotation of objects. The results of the study showed that using CAS in a calculus course had a positive effect on developing students' spatial visualization abilities. The results also showed that spatial visualization skills can be a predictor for success in a calculus course. The results have some important implications for education. First is that spatial visualization skills can be improved through training with relevant content. Second is that proper instruction by using some computer software such as MAPLE is effective for improving spatial visualization skills.