Run-time monitoring of SLA for Web Services Based Systems (WSBS) is an interesting as well as challenging topic in the field of web service monitoring. Several papers already address different aspects of the run-time monitoring. But most of the approaches are limited to composition layer (BPEL process). The behavior of composed web services is also affected by the behavior of other layers of the web service application domain. In particular, it is necessary to monitor the web services from the application layer. In this paper, the authors propose an approach to achieve run-time monitoring of SLA for WSBS at application layer.