A therapeutic approach utilizing animals is said to be effective for emotionally troubled patients. Recently, this animal-assisted therapy has been implemented in psychiatric hospitals. In the present study, patients seeking some kind of benefit from the interaction with animals participated, and their interaction with animals was closely observed. The results clarified the tendencies of those patients requiring this approach and the resulting changes in patients' mood. For the nurses engaged in 24-hour living support for hospitalized patients, environmental improvement is an important aspect of nursing care and “creating a hospital environment that includes animals” may be linked to emotional stability, improved motivation to live and environmental adaptation for patients who like animals.