The closed head impact (CHI) rat models are commonly used for studying the traumatic brain injury. Although various impact parameters (e.g., impact depth, velocity, and position) have been investigated by a number of researchers, little is known about the effects of the impactor shape, diameter, and material on the internal responses of the rat brain. In this work, numerical CHI experiments were conducted to investigate the sensitivities of intracranial responses to the impactor details such as impactor shape, diameter, and material. A 3D finite element rat head model with anatomical details was subjected to impact loadings. Results revealed that the impactor shape can affect the intracranial responses significantly. The effect of impactor diameter on the intracranial responses in different brain regions was uniform. In addition, careful attention should be paid when using an extremely compliant material for the impactor, since the actual impact depth might be compensated by the impactor deformation.