Companies are seeking more and more to offer customized goods and services to customers to be able to satisfy their needs. Several methods emerged to fulfill the needs of customization without affecting the performance of the company. Modularity has been considered as an effective method to address the challenges regarding variety management in the product and service domain. It has been addressed in the product domain but rarely in the service domain. This paper aims to provide a method to modularize a service-oriented system that consists of products and services. The method uses a set of modularization criteria and clustering techniques to form service-oriented system modules (product and/or service modules). The output of the clustering process is evaluated using indicators to provide decision-makers with insights into potentially preferred clustering alternatives. A test case is presented in order to show the applicability of the method.