Abstract. The penetration of smoldering combustion into the peat layer was experimentally studied taking into account a different botanical peat composition typical in the Tomsk region of Russia. The laboratory tests allowed us to obtain and analyze the temperature of the peat samples versus time, and also to estimate the velocity of the smoldering combustion in the horizontal and vertical directions. The results showed the faster penetration of smoldering combustion into the grass-sphagnum peat compared with the pine-cotton peat. The botanical composition and the flow of oxidizers in the combustion zone have a significant effect on the smoldering combustion, especially on the penetration of smoldering front into the peat layer. The chaotic distribution of the fuel particles contributes to the propagation of smoldering combustion both in the horizontal and vertical direction and influences on the spread of the smoldering front.