At the current development stage of computer networks, the emergence of new applications that use the high performance available is unavoidable. In this context, any service that requires high performance also requires network QoS (Quality of Service). To help the maintenance of QoS services and QoS provisioning mechanisms, this work proposes a QoS monitor. This monitor operates on IP-based networks and its goal is to measure current QoS parameters observed on the network and compare them with the negotiated QoS parameters. Thus, network managers can be informed about degradations, and proceed with proper actions in order to provide adequate conditions to applications that require strict time warranties in order to operate properly.