Sonepur Fair is organized every year on Kartik Poornima. Officially its start one day before Kartik Poornima. Duration of fair is around one Month, but apart from government stall, it runs around two month. Originally, the venue of the fair was Hajipur which situate across river Gandak(Narayani) and only the performance of the puja used to take place at the Harihar Nath temple of Sonepur. However, under the rule of the Mughal Emperor Aurangzeb, the venue of the fair got shifted to Sonepur. The temple of Harihar Nath is believed to have been originally built by Lord Rama, on his way to the court of King Janak to win the hand of Mata Sita. It is further said that Raja Man Singh later got the temple repaired. The Harihar Nath temple, as it stands today, was built by Raja Ram Narain, an influential person during the late Mughal period
It is considered as one of the World’s Largest Cattle Fair where you can find large number of elephants. Major attraction is the sight of numerous elephants, beautifully decorated. At present time elephant are not for sail, its only attraction. You will find a wide variety of goods in these stalls, ranging from garments, to weapons and furniture, toys, utensils and agricultural implements, jewelry and handicrafts. Various folk shows, games and jugglers can be seen in the fair.
The Fair also attracts International Visitors from various countries like US, Japan, France, Italy, Switzerland, Australia, Kazakhstan, Austria and many more.