Dosimetric characteristics of the FeMRI gels for various energy photon and electron beams were investigated using the Integrated Tiger Series (ITS) Monte Carlo codes. The FeMRI gels have been reported as being tissue-substitutes which can be shaped to any desired contour for three-dimensional (3D) mapping of dose distribution using magnetic resonance (MR) scanning. This study indicated that the central axis depth dose, off-axis depth dose, transverse profile at the depth of 50% of maximum dose, and energy deposition for photons and electrons in the gels are close to those in water. From these comparisons, it is concluded that FeMRI gels are suitable substitutes for water for the purposes of dose measurements of both photons and electrons used in radiotherapy.