The growth of seabird chicks is affected by various environmental conditions. Although species nesting in burrows may thereby reduce the effects of environmental conditions, they are still dependent on the nest microclimate. We investigated the influence of nest microclimate on chick growth in the little auk (Alle alle), a colonial High-Arctic seabird breeding in Hornsund (south-west Spitsbergen). We recorded air temperature inside and outside 10 active nests during two phases of breeding and during post-breeding period (no birds inside). We found that temperatures differed significantly among the nests. Air temperatures in nests located at higher altitudes were significantly higher, which can be attributed to the absorption of the Sun’s rays at a higher angle, resulting in a greater heat flux. Nest chamber temperatures were significantly higher (by 0.46°C) than ambient ones. During the post-breeding period, 24 hr cycle nest temperatures were more stable than ambient temperatures, indicating the important insulating function of nest burrows. Little auk chicks grew faster in nests with higher mean temperatures. In the first phase of chick growth (15th to 18th day of life), a 1°C difference in the nest temperature resulted in differences in head–bill length and body mass growth of 0.80 mm and 0.76 g per day, respectively. Our study demonstrates the importance of the thermal nest environment in determining chick growth in a species breeding in harsh High-Arctic conditions.