The aim of this study was to investigate the effects of dietary supplementation of acetaminophen on feed intake and growth performance of Hanwoo steers in the summer. Eight steers participated in a twelve-week experiment. The steers were randomly assigned into one of two treatments: Control and acetaminophen supplementation. Commercial acetaminophen was top-dressed to a concentrate mix at a rate of 3 g/kg based on dry matter. Individual feed intake was measured daily during the entire period of the experiment, and the intake of forage and concentrate diet were measured separately. The body weight of the steers were measured every 4 weeks. During the experimental period, ambient temperatures were recorded using an automatic temperature and humidity recorder. Acetaminophen had no effect (p > 0.05) on body weight, average daily gain, dry matter intake (DMI) and feed conversion ratio. Numerically, total DMI and concentrate DMI in the acetaminophen treated group were 5.7% and 7.6% lower than those of the control group, respectively, and the daily gain was 9.7% higher. As a result, the feed conversion rate of the acetaminophen treated group improved by 17% compared to the control; however, it was not statistically significant (p = 0.237). The results of this study suggest that acetaminophen supplementation may reduce the feed conversion ratio of Hanwoo steers under high temperature stress. However, further studies are needed to confirm the optimal level of acetaminophen supplementation which has a significant effect on the intake and weight gain of Hanwoo steers in the summer.