Provided is a QoS control system, a QoS control method, and a program suitable for use in a server virtualization environment in which an I/O virtualization technology can be used. The QoS control system includes a network interface and a network interface management unit. The network interface holds a QoS (Quality of Service) parameter giving identification information for identifying traffic, a priority value to be applied to a packet belonging to the traffic, and information indicating the storage location of the priority value in the packet, stores the priority value in the packet belonging to the traffic, and then transmits a resulting packet. The network interface management unit holds a QoS policy including a QoS parameter to be applied to each traffic, and manages the network interface.