PURPOSE: The gut microbiome is a major factor that can affect health and immunity. The purpose of this study was to analyze the effect of aerobic exercise for 4 weeks on changes in the intestinal microbiome. METHODS: A total of 24 men participated; Non-Exercise Group (NEG, 28.6 ± 5.3 yrs, 176.0 ± 7.8 cm, 81.3 ± 14.6 kg), and Exercise Group (EG, 28.6 ± 5.1 yrs, 175.5 ± 4.4 cm, 76.6 ± 10.6 kg). For the inclusion in the study, their physical activity level, intestinal health status, disease prevalence, medical history, and eating disorder were assessed. The basal level of gut microbiome in all participants was examined by stools collected one morning after a 10-hour fasting. EG performed more than 30 min of aerobic exercise per day, 3 or more days per week, for 4 weeks at a moderate intensity predicted from the maximal aerobic capacity test. After 4 weeks of training in EG, samples of gut microbiome were collected. Data analysis was performed using Wilcoxon. RESULTS: EG increased Bacteroidetes (44.16 ± 16.66 % in pre, 54.55 ± 12.30 % in post) and decreased Firmicutes (48.90 ± 14.32 % in pre, 39.38 ± 11.60 % in post) (p < .01). In EG, species of Bacteroidetes; Bacteroides_dorei (9.561 ± 7.408 % in pre, 12.483 ± 10.247 % in post) and Alistipes_indistinctus increased (0.000 ± 0.000 % in pre, 0.013 ± 0.031 % in post) (p < .05). Species of Firmicutes; Streptococcus_salivarius (0.095 ± 0.092 % in pre, 0.036 ± 0.038 % in post), Eubacterium_desmolans (0.352 ± 0.278 % in pre, 0.209 ± 0.175 % in post), Blautia_wexlerae (1.035 ± 1.022 % in pre, 0.670 ± 0.933 % in post), Coprococcus_catus (0.069 ± 0.079 % in pre, 0.029 ± 0.044 % in post), Coprococcus_comes (0.165 ± 0.203 % in pre, 0.082 ± 0.093 % in post), Dorea_longicatena (0.157 ± 0.157 % in pre, 0.058 ± 0.109 % in post), Roseburia_faecis (2.377 ± 2.176 % in pre, 1.842 ± 3.031 % in post), Caproiciproducens_galactitolivorans (0.128 ± 0.147 % in pre, 0.095 ± 0.095 % in post) (p < .05), Dorea_formicigenerans (0.063 ± 0.077 % in pre, 0.018 ± 0.036 % in post), and Veillonella_dispar (0.466 ± 0.817 % in pre, 0.126 ± 0.241 % in post) decreased (p < .01). CONCLUSIONS: The results showed that the beneficial bacteria increased and chronic disease-causing microorganisms were reduced by aerobic exercise. Supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea(NRF-2021R1A6A3A01086909)