Heat stress has an important effect on the welfare of livestock and causes significant changes in biological functions. This study was carried out to investigate the behavioral differences of Brown Swiss (BS) and Holstein (H) feedlot cattle reared in a hot environment. All of the cattle were housed in a semi-open feedlot barn. The individual behavioral response variables measured were feeding, drinking, rumination, standing, resting, locomotor activity and elimination (urinating and defecating). For each animal, behavioral observations were recorded at 10 mm intervals for 1 h starting at 06:00, 10:00, 13:00, 16:00, 20:00 and 23:00 h. The effect of breed, time of the day and hour of observation and the interactions of these factors were included in the model. The data were analyzed using the PROC GLM procedure in SAS. There were significant interactions between breed and time of observation for rumination (p < 0.001), standing (p < 0.001), resting (p < 0.01), time of feeding and locomotor activities (p < 0.05). Overall, feeding behavior was greater for BS cattle (p < 0.05). Resting behavior was greater for H (p < 0.01) and was primarily observed late at night (23:00 h). The observed effects of breed on behavior within the observation times from 06:00 to 23:00 h were significant (p < 0.05 and p < 0.001) except for the hour of observation beginning at 10:00 h (p > 0.05). BS cattle exhibited more frequent standing behavior at 13:00 h, whereas H cattle exhibited more frequent standing behavior at 16:00 h (p < 0.01). The welfare of male H feedlot cattle was concluded to be more affected than that of male BS feedlot cattle when the ambient temperature was high (at 13:00 h).