Software-as-a-Service (SaaS) is bringing new revolution to IT industry. SaaS has changed the way Software developed, deployed and maintained. SaaS eliminates the requirement of customers (tenants) to purchase, install and maintenance of infrastructure and software. Customers only have to pay for services provided by SaaS vendors. Multi-tenancy in SaaS application is most important feature for the success of SaaS application. However there are many challenges in the development, deployment, and security of such application. This paper addresses the issue of how to effectively support multi-tenancy in SaaS application and proposes SaaS architecture to support multi-tenancy in e-commerce application.