The present invention provides a manifold insert having a plurality of distribution guides which reduce output voltage deviation due to flow instability between unit cells and prevent local flow instability of electrodes by stably distributing the flow of fluid (such as air, hydrogen, and coolant) supplied to a fuel cell stack, thereby maintaining a stable performance of the unit cells, and a fuel cell stack comprising the same. In particular, manifold insert having distribution guides is provided, the manifold insert being configured to form a flow field from an inlet port of fluid to an outlet port connected to a fuel cell stack, the manifold insert including: a plurality of distribution guides for dividing the flow field from the inlet port to the outlet port such that the fuel cell stack is divided into a plurality of regions according to the distance from the inlet port, wherein the distribution guides have surfaces that are at least partially curved such that the flow of the fluid from the inlet port to the outlet port is changed by the curved surfaces and form a plurality of guide flow fields for guiding the fluid to the divided regions of the fuel cell stack such that the fluid is supplied to the divided regions of the fuel cell stack along the plurality of guide flow fields at different flow rates.