A manifold block assembly for a fuel cell vehicle mounted on a fuel cell stack and supplying air and hydrogen to the stack, includes a manifold block in which a hydrogen discharge path connected to a hydrogen line formed in the stack, an air discharge path connected to an air line formed in the stack, and a watertight bulkhead are integrally formed with each other. The manifold block assembly further includes a hydrogen inflow pipe configured to be attached to the manifold block and connected to the hydrogen line formed in the stack. The manifold block assembly also includes an air inflow pipe configured to be attached to the manifold block and connected to the air line formed in the stack.