We investigated the floristic composition of the Hyrcanian forests and the related forest-steppe ecotone in Northern Iran by using two long ecological transects, from lowland to upper mountain areas. The study was conducted during 2008 and 2009 and yielded the identification of 395 plant taxa belonging to 233 genera and 78 families. Dicots with 300 taxa were the richest groups of the flora, followed by monocots with 75 taxa, pteridophytes with 18 species,and gymnosperms with two species. The largest families were Asteraceae(33 taxa); Rosaceae(32 taxa); and Poaceae(30 taxa), and the most diverse genera included Carex(15 taxa); Alchemilla(7 taxa); and Poa, Geranium and Acer(6 taxa each). Hemicryptophytes were the most dominant life forms in the area(40 %); followed by geophytes(31.4 %); phanerophytes(15.4 %); therophytes(11.4 %); and chamaephytes(1.8 %). Phytogeographically,Euro-Siberian/Irano-Turanian elements(86 taxa, 21.8 %)and Euro-Siberian elements(85 taxa, 21.5 %) were the most common chorotypes in the area. Out of 395 taxa, 66taxa(16.7 %) were endemics and subendemics in Iran, of which 26 taxa were exclusively endemics of Iran.According to the IUCN Red List Categories, 48 threatened plant taxa were found in the study area. Plant diversity, life form, and chorotypes in the current study were compared with similar transect studies in other areas of the Hyrcanian forests and in different altitudinal belts, using S?renson similarity indices. Floristic composition of the surveyed transects demonstrated almost 50 % similarity between them. We investigated the floristic composition of the Hyrcanian forests and the related forest-steppe ecotone in Northern Iran by using two long ecological transects, from lowland to upper mountain areas. The study was conducted during 2008 and 2009 and yielded the identification of 395 plant taxa belonging to 233 genera and 78 families. Dicots with 300 taxa were the richest groups of the flora, followed by monocots with 75 taxa, pteridophytes with 18 species, and gymnosperms with two species. The largest families were Asteraceae (33 taxa); Rosaceae (32 and Poaceae (30 taxa), and the most diverse genera included Carex (15 taxa); Alchemilla (7 taxa); and Poa, Geranium and Acer (6 taxa each). Hemicryptophytes were the most dominant life forms in the area (40%); followed by geophytes (31.4%); phanerophytes (15.4%); therophytes (11.4%); and chamaephytes (1.8%). Phytogeographically, Euro-Siberian / Irano-Turanian elements Euro-Siberian elements (85 taxa, 21.5%) were the most com mon chorotypes in the area. Out of 395 taxa, 66taxa (16.7%) were endemics and subendemics in Iran, of which 26 taxa were exclusively endemics of Iran. According to the IUCN Red List Categories, 48 ​​threatened plant taxa were found in the study area. Plant diversity, life form, and chorotypes in the current study were compared with similar transect studies in other areas of the Hyrcanian forests and in different altitudinal belts, using S-renson similarity indices. Floristic composition of the surveyed transects- similarity between them.