Contractual relation between customers and telecommunications service providers are becoming increasingly complex, due largely to changes in the marketplace and growth in the number and complexity of services on offer. In order to guarantee a certain quality of offered service and in response to customer needs, some mechanisms of service level management must be applied. The service level management in telecommunication networks is made by a agreement, established during the service subscription, which is used by customers and service providers to control the service level. This paper introduces a service level management system for ATM networks, which can be applied to different telecommunication systems.