A biologically motivated mathematical model of the dynamics of the small intestinal epithelium in humans treated with fractionated radiotherapy has been developed and is further investigated here. This model, originating from our previous work, is implemented as a system of nonlinear ordinary differential equations, in which the variables and parameters have a clear biological meaning. The model also includes, as input, the key parameters of fractionated irradiation. The modeling results on the dynamical response of the human normal small intestinal epithelium to fractionated radiation therapy regimens were in agreement with the corresponding empirical data, which, in turn, demonstrates the capability of the developed model for predicting the dynamics of this vital body system in humans receiving fractionated radiotherapy. It is also revealed that the cumulative damage effects of hypofractionated radiation therapy regimens on the human normal small intestinal epithelium are somewhat less pronounced than those of conventional fractionated radiation therapy regimens with the same total doses.