In developing countries small and medium scale enterprises are highly important for economic growth and creating employment. But due to financial, economic and man power constraints, implementations of complex and expensive packaged software like proprietary ERP to gain operational efficiency is critical for these SMEs. In such context adoption of open source ERP can be beneficial both in terms of cost effectiveness and efficiency. Though IS literature has a rich contribution towards understanding the adoption of proprietary ERP software, very less focus has been given for open source ERP (OS ERP) implementation. To address this gap and considering the practical importance for SMEs, this research in progress paper focuses on factors that influences the adoption of OS ERP in SMEs. This paper uses the theoretical framework designed by Macredie & Mijinyawa for exploring the underlying factors and their influence on Open Source Software adoption to understand the adoption of OS ERP. This proposed framework is an extension of the Decomposed Theory of Planned Behavior specifically in the context of understanding adoption in SMEs.