The analysis of biological activity of soils in the conditions of permafrost on the example of north taiga larch forests of Central Evenkia on the slopes of northern and southern exposures was carried out. To assess the role of pyrogenic factor in the formation of biological activity of soils on the slopes of southern exposure, a number of different post-fire fires (1, 2 and 24 years) were selected. Larches of the older post-fire age were considered as condi-tionally undisturbed and control areas. Soils were represented by podburs and cryosems. Soil for-mation in the north taiga subzone was limited by two main factors: the features of the parent rocks and permafrost. North-taiga larch forests have a complex microrelief. At the placer sites and on the slopes of northern exposition, a combination of microincrements and microdepressions was clearly pronounced. Such differences cause spatial heter-ogeneity of moss-lichen layer and litter. To charac-terize the activity of biological processes, soil en-richment by enzymes catalase and urease and cel-lulose-decomposing activity in situ were assessed. The soils for enrichment with enzymes catalase and urease were characterized as poor and very poor (according to the scale of Zvyagintseva D.G.). The low activity of integral characteristic of biologi-cal processes was shown: cellulose decomposition: no more than 7 % of cellulose decomposes in three months. In the first years after high-intensity fires, stimulating effect of pyrogenic factor on enzymatic and cellulose-decomposing activity of cryogenic soils was revealed, which was especially pro-nounced in the upper pyrogenically transformed layers.The analysis of biological activity of cryogen-ic soils in the larch forests of northern taiga has shown that pyrogenic factor differs more strongly in the intensity of biological processes than in micro-climatic conditions of the studied habitats.