The influence of moorshing processes of peat soils on nitrogen adsorption and on specific surface area was investigated. Soil samples for study were taken from differently moorshified peat-moorsh soils, characterizing by W1 index ranged from 0.44 to 0.82. The samples represented two kinds of moorsh fonnations, i.e., peaty moorsh (Z₁) and propert moorsh (Z₃). Nitrogen adsorption measurements at 77 K were used for determining the surface area and pore volume. The Brunauer-Emmett-Teller (BET) method was used as the standard procedure for determination of the surface area. The adsorption and desorption isotherms of N₂ on peat-muck soils at 77 K exhibited similar shape and all belonged to the type II, according to BET classification. The adsorption increased in the series of the soil samples Nos 11<1<13<12 and 10<5<6<8 for the peaty moorsh (Z₁) and for the proper moorsh (Z₃), respectively. The above series agreed with the changes of the index of the secondary transformation, W₁, except for the samples Nos 12 and 5. The nitrogen-BET specific surface area of soil samples ranged from 2.45 to 4.90 m² g^–1, and no direct relation between the surface area and the index of the secondary transformation, W₁, was found. When soil samples are first grouped into the classes Z₁ and Z₃, and then, for each group, arranged according to the value of the index W₁, the relationship between W₁ and the specific surface area became more visible. Generally, for the proper moorsh (Z3), an increase of the nitrogen-BET surface area and a decrease of the pore volume were correlated with the increase of the W₁ index (except for the samples Nos 8 and 5). In the case of the peaty moorsh (Z₁) a decrease of the nitrogen-BET surface area and an increase of the pore volume were connected with the increase of the W₁ index, (except for the samples Nos 12 and 13).