The magnetic phase transitions in LaMn2-xFexSi2 (0.0 less than or equal to x less than or equal to 1.0) silicides were studied by X-ray diffraction, differential scanning calorimetry techniques and AC magnetic susceptibility measurements. All compounds crystallize in the ThCr(2)Si(2)type structure with the space group I4/mmm. The lattice constants and the unit cell volume obey Vegard's law. For the samples with x less than or equal to 0.4 the ferromagnetic interactions within the Mn sublattice occurs below the Curie temperature (T-C(Mn)). The Curie temperature was depressed linearly by the substitution of Fe for Mn. The temperature dependence of the AC susceptibility shows a distinct feature for the samples with x less than or equal to 0.3 below T-C(Mn). These samples have a mixed state composed of ferromagnetic and anti-ferromagnetic phases. The samples with x greater than or equal to 0.6 have the Neel temperature below the room temperature, while the other samples are anti-ferromagnetic above the room temperature. The results lead to the construction of the partial magnetic phase diagram. (C) 2004 Elsevier Ltd. All rights reserved.