Although the unified modeling language (UML) is becoming the de facto industry standard for object-oriented system development, it is not short of critics. Both researchers and practitioners have agreed that much work needs to be done to enhance UML. This research evaluates the nine UML diagrams using GOMS. GOMS, beginning as a theoretical model in HCI, describes the procedures required for accomplishing a general set of tasks by decomposing the tasks into four elements: Goals, Operators, Methods, and Selection rules. We use a special type of GOMS, NGOMSL, for analyzing UML. This research attempts to find ways to enhance the ease of use of UML diagrams and contribute to the evolution of UML.