Abstract: An information processing system includes: an activity acquiring unit that acquires an activity amount from a sensor mounted on an animal; a storage unit that stores the previously acquired activity amount corresponding to datetime; a behavior identifying unit that identifies a behavior of the animal by frequency analysis of the activity amount; a vitality disappearance determining unit that determines whether the vitality of the animal has disappeared according to whether the activity amount on a particular day is less than a first threshold defined by the activity amount in a period prior to the particular day and whether a number of times or time length of the predetermined behavior on the particular day is less than a second threshold defined by the number of times or the time length during the period; and a notifying unit that notifies that the vitality has disappeared.