Temperatures were measured to 2 m depth at six peatland sites in the Schefferville area, northern Quebec, from July 1982 to September 1984. The sites varied in their plant cover, type of peat, and depth of snow, and two sites represented string and flark morphology. During the summers, the surface layers (5 – 10 cm) reached temperatures of 15–20 °C and the 10 °C isotherm reached depths of 50–150 cm, depending on the site characteristics and the influence of the preceding winter conditions. The progression of the 10 °C isotherm downwards could be predicted from climatic variables, such as cumulative thawing degree-days. During the winter, the 0 °C isotherm reached depths of between 20 and 90 cm, based primarily on the thickness of the insulating snowpack and its development during the winter. The surface layers (5 – 20 cm) of the peat remain close to freezing (−1 to −3 °C), despite the very cold air temperatures (−20 to −30 °C). Examination of a cooling and a warming sequence at the string and flark sites reveals that the string near the surface is about 2 °C colder than the flark during the winter, and that during the early summer it can be 8 – 14 °C warmer than the flark. Differences in thermal regimes between sites and between seasons are interpreted in terms of the major climatic factors and the characteristics of the sites.