Nipah virus (NiV), emerged in Peninsular Malaysia, caused an outbreak of severe febrile encephalitis in humans and respiratory diseases in pigs between 1998 and 1999. By May of 1999, the death of 105 humans and the culling of about 1.1 million pigs were reported. Fruitbats of Pteropid species were identified as the natural reservoir hosts. The epidemiological studies suggested that NiV was introduced into pig farms by fruitbats, and was than transmitted to humans (mainly pig farmers) and other animals such as dogs, cats and horses. In 2004, NiV reappeared in Bangladesh with greater lethality. In contrast to the Malaysia case, epidemiologic characteristics of this outbreak suggested the possibility of fruitbats-to-person, or person-to-person transmission. In this article, the epidemiological comparison between two outbreaks in Malaysia and Bangladesh, and the new-trends of virological studies of NiV will be discussed.