The invention relates to a railway vehicle (1) comprising in its underframe (U) a LNG storage and supply system (S), the system (S) comprising a box (7) and a plurality of LNG tanks (2) arranged in the box (7), wherein the box (7) is attached to the underframe by means of fixation assemblies (10) and the LNG tanks (2) are attached to the underframe (U) by means of fixation assemblies (10), such that the box (7) and the LNG tanks (2) are independently fixed to the underframe (U). The invention also relates to a method for mounting said LNG storage and supply system in the underframe of a railway vehicle.