Lalejin District (Persian: بخش لالجین) is a district (bakhsh) in Bahar County, Hamadan Province, Iran. At the 2006 census, its population was 44,568, in 10,635 families. The District has two cities: Lalejin and Mohajeran. The District has two rural districts (dehestan): Mohajeran Rural District and Sofalgaran Rural District.