The aim of this study was to investigate the effects of web-based interactive virtual tours on the development of prospective mathematics teachers' spatial skills. The study was designed based on experimental method. The "one-group pre-test post-test design" of this method was taken as the research model. The study was conducted with 3rd year students of department of mathematics teaching for primary schools in a state university, who had taken computer courses for two terms but hadn't been involved in a web-based interactive virtual tour before. A total of 60 teacher candidates were included in the study. The Purdue Spatial Visualization Test (PSVT) was administered as the pre-test and the post-test. This test was developed so as to consist of 36 multiple choice items and include the skills of mental visualization of objects based on their surface developments, mental rotation of objects and mental visualization of rotated views of objects. In conclusion, according to the findings, the greatest increase occurred in developments part of prospective primary school mathematics teachers' spatial skills. Secondly, there was an increase in the rotations part. Next, the lowest increase was found in the views part. (Contains 8 figures and 6 tables.)