Introduction: Several studies have analyzed the benefits of High Intensity Circuit Training (HICT) in some cognitive function such as short-term memory. However, the effect of long-term and regular HICT particularly in young adults, who need good cognitive function including attention function to improve the learning process, has not been studied yet. This study is aimed to analyze the effect of regular HICT in attention function improvement of young adults. Methods: This study was a quasi-experimental study with pre-test and post-test un-equivalent group method. Samples were taken purposively from medical student of Diponegoro University (n=56, age=18-22 years old), who were divided into two groups, the control and training group. Attention Network Test (ANT) was used to measure attention function in alerting, orienting and executive function before and after HICT. The data were analyzed using Paired t-test, Independent t-test, Wilcoxon test, and Mann-Whitney test. Results: A significant improvement of attention function was found in executive function and reaction time after High Intensity Circuit Training for 8 weeks (p<0.05), with mean 15.67ms to 14.36ms; 620.46ms ± 110.13 to 573.14ms ± 67.11, respectively. The mean difference between pre-test and post-test attention function test was found increased in alerting, executive function and reaction time (p>0.05), that training group had higher score as compared to control group, with mean difference 0.7857ms; 31.3ms; 30.29ms, respectively. Conclusion: Regular High Intensity Circuit Training improves attention function particularly in executive function and reaction time in male young adults.