A valve assembly for an injection valve and a method for assembling a valve assembly are provided. The valve assembly includes a valve body with a central longitudinal axis and having a cavity with a fluid inlet portion and a fluid outlet portion, an end portion being arranged at an axial end facing away from the fluid outlet portion, and a seat being arranged at an axial end of the valve body facing the fluid outlet portion. A valve needle is axially movable in the cavity and prevents a fluid flow through the fluid outlet portion in a closing position and releases the fluid flow through the flu-id outlet portion in further positions. The valve needle has an axial end facing away from the fluid outlet portion and facing the end portion, and a seat part resting on the seat of the valve body in the closing position. A contact area between the seat part and the seat of the valve body has a first outer diameter. The valve assembly includes an electro-magnetic actuator unit being designed to actuate the valve needle. A bellow arrangement includes a bellow and an end portion, the bellow is fixedly coupled to the end portion in a coupling area. The coupling area has a second outer diameter. The first outer diameter is equal to the second outer diameter.