The phenomenon of evolution is closely related to Open Source Software (OSS) as there is a frequent release of versions. Improvements to the software are due to the enormous contributions made by developers. Software reusability is also seen as a necessary characteristic of OSS. In this paper, a conceptual model for reusability assessment is presented and reusability of the software is studied during evolution. The attributes of reusability of different versions are assessed and compared. The relationship between the attributes of reusability is analyzed. The experiment conducted in this paper is one of the potential applications of our proposed reusability assessment model. The study helps to understand the evolution of software from the perspective of reusability. The change in size (e.g. number of lines of code; number of methods/classes), maintainability index complexity, etc. are studied in different versions to analyze their effect on reusability of the software. The results justify the proposed reusability attribute model. © 2012 IEEE.