To provide a fan shroud for an onboard heat exchanger capable of efficiently securing air quantity in the fan shroud with a part of a cooling fan protruded to an upper side of a core of the heat exchanger.

When a ratio of a part covered with the fan shroud 13 from a blade part front end of the cooling fan 2 to a blade part rear end is determined as a covering ratio, a covering ratio of a ring part 3a protruding from a core part 1a of the cooling fan 2 is set to be smaller than covering ratios of a ring part 3b which does not protrude from the core part 1a of the cooling fan 2 and a connecting part 3a. By making the covering ratio of the ring part 3a with high oblique flow tendency small and making the covering ratios of the ring part 3b with a comparatively small in oblique flow tendency and the connecting part 3c larger than the covering ratio of the ring part 3a, air quantity can be increased.