The study of ingestive behavior is a highly important tool in the evaluation of diets, because through it is possible to acquire knowledge of the possible relationships existing between foods and animal, allowing us to adjust the feeding management of animals to obtain better productive performance. The objective of this trial was to determine the effects increasing levels of concentrate on feeding behavior of lambs. Fifteen crossbred lambs (initial BW of 18.2 ± 3.2 kg and 100 d old) were used in a randomized complete block design according to initial BW and age. Lambs were penned individually during 45 d and fed an isonitrogenous (16.6 ± 0.55 CP, DM basis) diet. Increasing levels of concentrate were 40, 60, or 80% corresponding to the experimental diets C40, C60 and C80, respectively. Animals were monitored every 5 min during 24 h, on the 23th day of the experiment, according to the activities: eating, rumination, idle and other activities. The feed and rumination efficiencies, expressed as g DM/hour were obtained by dividing the average daily intake of dry matter by the total time spent eating and/or ruminating in 24 h, respectively. Orthogonal polynomials for diet responses were determined by linear and quadratic effects. Effects were declared significant at P ≤ 0.05. There was a quadratic response (P ≤ 0.05) for time spent in eating. The levels of concentrate did not affect (P ≥ 0.05) the eating efficiency (149.3, 182.3 and 226.1 g DM/h for C40, C60 and C80), time spent in idle (505.0, 493.0 and 589.0 min/d for C40, C60 and C80) and water intake (1.8, 2.5 and 2.5 kg/d for C40, C60 and C80). The time spent in other activities (133.0, 185.0 and 220.0 min/d for C40, C60 and C80) and rumination efficiency (92.4, 116.5 and 132.4 g DM/h for C40, C60 and C80) tended to linearly increase (P = 0.07) with high concentrate levels. However, the time spent in rumination (495.0, 462.0 and 391.0 min/d for C40, C60 and C80) tended to linearly decrease (P = 0.06) with high concentrate levels. It is concluded that high concentrate levels (C80) changed the feeding behavior of lambs, especially for time spent for eating