Objective: Acetic acid bacteria were traditionally used to produce fermented food. Furthermore, acetic acid bacteria contain unique membrane lipids that would be expected to attenuate inflammation. This study examined the effects of oral intake of acetic acid bacteria isolated from fermented milk on muscle damage after moderate-intensity exercise. Methods: In a double-blind placebo-controlled crossover trial, 40 untrained subjects (16 men and 24 women; age, 46.4 ± 4.3 yr; height, 162.8 ± 10.8 cm; weight, 60.2 ± 9.4 kg; body mass index, 22.6 ± 2.9 kg/m2) took 111 mg of dried acetic acid bacteria per day (supplemented group) or 111 mg of cornstarch per day (placebo group) for 1 week and walked for 60 min on the last day of administration. Results: Leukocyte, lymphocyte and neutrophil counts, IL-6 and creatine kinase (CK) activity, myoglobin (Mb) concentration and perceived pain in parts of the body were measured pre and post exercise. All values, except for IL-6, were significantly increased post-exercise compared with pre-exercise in both groups. However, neutrophil counts and ankle pain were significantly lower in the supplemented group. In addition, the increase of CK activity in the supplemented group was significantly attenuated at 24 h after exercise (supplemented group, 114 ± 54 U/l; placebo group, 126 ± 68 U/l). The supplemented group also demonstrated a trend toward a lower level of CK activity after exercise (p = 0.06). Other values did not differ between groups. Conclusion: These results suggested that acetic acid bacteria supplementation was useful to attenuate muscle damage after moderate-intensity exercise.