In order to manage financial risks online charging of composite services is becoming increasingly important for service providers to support service delivery in inter-domain environments. The 3rd Generation Partnership Project (3GPP) has developed a framework for off-line and online charging of IMS-based services. At service level, delivery of composite services often involves many service providers, where each service provider is responsible for the delivery of one or more service components (e.g. access service, IMS communication service, content service, etc.). Current Online Charging System (OCS) specified by 3GPPP does not support an online charging function for composite services. This paper discusses a number of implications of online charging of composite services, in particular inter-domain composite services. It addresses important shortcomings of the current 3GPP online charging architecture and suggests a way to overcome these shortcomings. The contribution of this paper is twofold. Firstly, it proposes an information model to support charging of inter-domain composite services. The proposed information model is based on the NGOSS and SID concepts of the TeleManagement Forum. Secondly, it proposes additional functionalities required for existing OCS in IMS to handle online charging of inter-domain composite services. © Springer-Verlag Berlin Heidelberg 2009.