The Media-on-Demand (MOD), derived from traditional Video-on-Demand, is a significant value-add service for operators in the present and the foreseeable future. This paper introduces a flexible content protection system for MOD, named On Demand Content Protection (ODCP). The ODCP system does not rely on the conventional conditional access system, and can be applied in both Internet and cable environment; it supports unicast and multicast content distribution; its player can be either an application on PC or a device such as a set-top box. In ODCP, contents are protected from end to end. A user cannot play the content without an entitlement from the MOD service provider. And a usage rule can be bound with the entitlement, so that the service provider can specify how and when the user could use the content.