Service Oriented Architecture (SOA) is becoming popular since its flexibility fulfill the need of rapidly changing enterprise requirement. Therefore, expectation of a good quality software with SOA is getting higher. To address this need, this paper presents a guideline to conduct quality assessment using an existing tool. The quality assessment model is designed by selectingthe relevant quality factors, choosing an appropriate quality to metric mapping method, identifying the relevant metrics, and mappingeach quality factor to the metrics.Using the model, the quality assessment process is prepared by identifying data and selecting the appropriate tools.The chosen tool may require some modification.The proposed quality assessmentguideline can help the software quality assurance team to assessquality of their software with SOA. The proposed guideline has been used to assess the quality of an existing sofware with SOA (Bonita BPM). The result is considered as promising, although several improvement are still needed.