To provide a method for retort sterilization of pouches with mouths, capable of preventing pollutant of e.g. powdered dust from depositing between the mouth and cap and apart from the fear of breaking the hermetic seal of the pouch.

This retort sterilization method for pouches 10 with mouths 3 each comprising a hermetic seal 5 applied onto the opening 32 of the mouths 3 serving to send out the stuff in the pouch 10 and a cap 6 covering the hermetic seal 5, comprises: sequentially engaging the pourers 3 with an engaging member 7 attachable to and detachable from the mouths 3 for forming a bundle 11 of a plurality of pouches 10 supported by the engaging member 7; wet-heating the bundle 11 in a retort; and covering the mouths 3 of the wet-heated pouches 10 with the caps 6.