Bat, the only flying mammal and count more than 20% of the extant mammals on earth, were recently identified as a natural reservoir of emerging and reemerging infectious pathogens. Astonishing amount (more than 70) and genetic diversity of viruses isolated from the bat have been identified in different populations throughout the world. Many studies focus on bat viruses that caused severe domestic and human diseases. However, many viruses were found in apparently healthy bats, suggesting that bats may have a specific immune system or antiviral activity against virus infections. Therefore, basic researches for bat immunology and virus-host interactions are important for understanding bat-derived infectious diseases.