Three new species of Lejeunea (Lejeuneaceae) from Papua New Guinea are described and illustrated herein. They are L. heinarii, L. madangensis and L. marginedentata from Morobe, Madang and Sandaun (West Sepik) province, respectively. They were found growing as epiphytes on trees and inhabit the montane forests of the island. Lejeunea heinarii is characterized by the strongly inflated and inrolled leaf lobules, large reniform underleaves with retuse apices, and well-developed trigones with conspicuous intermediate thickenings (up to 4 per cell), while the distinguishing characters of L. madangensis are the 2-winged perianth keels, large reniform underleaves with cordate-auriculate bases, flat free margin of leaf lobules, and autoicy. Lejeunea marginedentata stood out among all its allies by the inflated perianths without keels, asymmetrical leaf lobes with strong arched dorsal margin and straight ventral margin, and the prominent dentate margin with acute teeth.