The moss and liverwort flora of Zackenberg valley in the Northeast Greenland National Park has been studied based on field investigations and literature survey. Altogether 212 taxa are recorded in the area, with 43 liverworts and 169 mosses. Five taxa are reported as new to Greenland Lophochaete fryei (Perss.) R.M. Schust., Sphagnum orientale L.I. Savicz, Orthothecium lapponicum (Schimp.) C. Hartm., Pohlia vexans (Limpr.) H. Lindb. and Tortella alpicola Dixon. Additionally four taxa are reported as new to east Greenland; Grimmia plagiopodia Hedw., Riccardia latifrons (Lindb.) Lindb. Sphagnum olafii Flatberg and Tritomaria exsectiformis (Breidl.) Schiffner ex Loeske. The bryophyte flora of the Zackenberg valley is characterised by pioneer species adapted to disturbance by frost and wind, but also more stable communities exist especially at the lower part of the valley with wet to moist tundra. The Zackenberg valley bryophyte flora shows higher similarity with the flora on Svalbard (81%) compared with Ellesmere Island (67% and 60% for liverworts and mosses, respectively). This is consistent with east Greenland and Svalbard belonging to the North Atlantic Arctic flora province while Ellesmere Island belongs to the Canadian Arctic flora province.