The missions of complex systems, organizations, or groups can be identified through careful requirements and domain analysis. Mission architecture modeling is a crucial step for enterprise modeling and design. However, mission modeling is lacking from the Unified Architecture Framework (UAF), which system engineers must specify and model from sketch. This paper proposes a Mission Architecture Modeling Language (MissionML). This two‐layer architecture language generalizes the general common and special knowledge from four typical missions as a core layer and mission layer. The elements of the core layer are obtained through slight extensions of the operational layer elements in UAFML, and the elements of the mission layer are derived from the elements in the core layer. Moreover, MissionML is implemented as a UAF profile, incorporating numerous domain concepts in its syntax and semantics for mission modeling. Finally, we use five public case studies to demonstrate learnability and extensibility from the viewpoint of system engineers.