The main purpose of this research was to construct a mathematical model of work curve of Uchida-Kraepelin Psychodiagnostic Test (UKPT). The proposed model is composed of 2 components, i.e., learning and fatigue. The theoretical curve including 5 parameters was derived from the model, and Marquardt's method was used to estimate these parameters. Estimation of 5 parameters can be performed for each individual's work curve. The examination of validity of this model was the problem left for the future.