Lahan is a town and municipality in Siraha District in the Sagarmatha Zone of south-eastern Nepal. At the time of the 1991 Nepal census it had a population of 19,018 people living in 3622 individual households. Famous Sarda Group of nepal hail originally from this town and people respect the Sharda family a lot for their contributions to town. The town is close to Indian border town of Laukaha. Famous Sarda RICE and Oil mill is in the Nepal Side of Border at Thadi Biswaspatti. An engineering college is planned at this location but is stoppend currently due to poor law and order condition of Nepal.