The study aimed to evaluate the behaviour of beef cattle reared in intensive systems in northern Italy under different climatic conditions. In particular, it considered 3 levels of THI (Temperature-Humidity-Index) in order to evaluate the coping response to heat stress conditions regarding changes of beef cattle nutritional and social behaviours, drinking frequency and resting time. Behavioural observations were carried out from July to October 2005, during hot (THI above 78), mild (THI 76) and cool (THI below 72) conditions, on 24 finishing French crossbred bulls. The animals were housed in 6 fully slatted floor group pens of 4 bulls each. Within each class of THI, behaviours were recorded in two sessions of 24 hours using a 5 minute interval scan sampling technique. A focal animal was chosen in order to count the number of visits at the waterer. Results showed that eating behaviour was maximum during the first 8 hours after fresh feed delivery. However, in the same interval, when THI was above 78, eating activity was penalized while an increase of ruminating was observed. The overall number of visits at the waterer was increased by the heat stress condition and they were mainly concentrated in the hottest hours of the day. Hot environment also affected beef cattle social behaviour increasing agonistic interactions and mounts among penmates. Since heat stress affected bulls behaviour impairing their welfare, the adoption of cooling devices should be recommended.