Urbanisation imposes new constraints on organisms, leading to changes in various traits including behaviour. In particular, foraging and aggressive behaviours are often affected by urbanisation. In eusocial species, behaviour can be defined at the individual level but also at the group level (colony), and only a few studies have investigated how urbanisation may affect colony-level behaviours. In this study, we compared the aggressive and foraging behaviours at the colony level between city and forest populations of the ant species Temnothorax nylanderi. We collected colonies in three urban parks and in three forests. After two weeks of acclimation to the laboratory, we investigated foraging traits (the mean number of foragers feeding on the food, the food discovery time, and the number of food-to-nest trips) by introducing food in the foraging area for three hours. Two weeks after the foraging experiment, the level of aggressiveness was measured for the same colonies by introducing the body of a frost-killed conspecific in the nest. We found no differences between city and forest colonies for the mean number of foragers and the discovery time. However, we found that city colonies performed more foraging trips than forest colonies, and that city colonies were less aggressive. Interestingly, foraging and aggressive behaviours were positively correlated in city, but not correlated in forest colonies. This study is one of the few addressing the question of behavioural divergence at the group level in response to urbanisation in ants. It corroborates what was found at the individual level in non-social species.