Software as Service (SaaS) model of cloud computing is currently one of the most advanced technology innovations. Due to its scalability and network-based operation, SaaS offers opportunities for small and medium enterprises (SMEs) to take advantage of the latest technology without costly investment on IT infrastructure and expertise. Despite its benefits, SMEs’ adoption of SaaS is not prevalent. In this paper, by synthesizing Diffusion of Innovation theory, Technology-Organization-Environment theory and Protection Motivation theory, we propose a conceptual model which explains adoption factors of SaaS in SMEs. Our proposed model extends focus on protection motivation of SMEs in assessing SaaS adoption risks in addition to technology, organisation, and environment factors.