This study evaluated the impact of mixing cattle from two sources of feedlot steers (n = 96) on feeding and lying behavior. Angus crossbred steers (n = 48 McG and n = 48 BCS), similar in genetic composition, were transported (833.64 85.29 km) to a feedlot 39-d prior to mixing where the two sources were housed without visual or tactile contact. Steers, blocked by source and stratified by d -34 body weight, were randomly assigned to one of 12 pens (n = 8 steers/pen) for the 42-d study. Pens were assigned to one of two treatments (n = 6 pens/treatment): 1) NOMIX100% of cattle from McG (n = 3 pens) or BCS (n = 3 pens) and, 2) MIX50% of cattle from BCS and 50% from McG (n = 6 pens). Instantaneous scan sampling (n = 61 scans/d; 10 min intervals) recorded the number of steers per pen eating and lying on d1, 2, 3, 4, 5, 6, 7, 8, 9, 14, 15, 16, 21, 22, 23, 28, 29, 36, and 37 after mixing. Proportion of steers lying varied across time (P > 0.0001); however, a greater proportion of steers laid down on d1 compared to d7, 8, 9, 16, and 28 (P > 0.03). The proportion of steers observed eating increased over time (P > 0.0001). Fewer steers ate on d1 than d9, 14, 15, 28, 29, and 36 (all P > 0.01). More steers were observed eating on d8 and 16 than the first seven days (all P > 0.01) and on d37 than the first 6 days (all P > 0.02). While there was no impact of mixing, data indicate that handling and sorting cattle into new pens impacts eating and lying behavior and it takes approximately a week for behavior to stabilize.