The adoption of Open Source products among expert users has been high over the years. Open Source Software (OSS) development tools and server applications have also been gaining popularity. There is however a significant lag in the uptake of desktop open source software especially by ordinary users in Africa. Usability issues have been raised as a major hindrance to the adoption of desktop OSS products. The objective of this paper is to present the results of OSS adoption levels by Kenyan university students and also to establish the effect of usability on adoption of Open Source desktop operating systems and applications by university students in Kenya. The empirical study revealed that in the absence of software piracy, OSS adoption is positively influenced by its usability.