Our research group found that zoological garden is a resourceful place for learning by experience, so that we set "ZOO PROJECT" that aims at reconstructing learning environment for children in zoo, by using emerging information technology such as mobile phones, Podcasting and interactive website. As the first attempt, we developed Voice Trackback System, a collaborative voice data gathering system for learning by experience. Users report their thoughts and impressions by their own voices with mobile phones, after observing animals. Voice data is collaboratively gathered in a PC server by Skype, an IP phone network, and then displayed on a project website. Users can listen to the voices respectively and freely. This system is constructed on the viewpoint of "Learning by Teaching". It is hoped that the participants learn the animals and nature by reporting and also by listening to others' voice reports.