Probiotic bacteria exhibit a variety of properties, which are unique to a particular strain. Lactobacillus acidophilus-SDC 2012, 2013 are new strains isolated from Korean infants' feces. The potential utility of Lactobacillus acidophilus-SDC 2012, 2013 in irritable bowel syndrome (IBS) was studied. Forty IBS patients were randomized into a placebo (n = 20) and probiotics group (n = 20). Four weeks of treatment with L. acidophilus-SDC 2012, 2013 was associated with a reduced score for abdominal pain or discomfort compared to the baseline (P = 0.011). The percent reduction in abdominal pain or discomfort exceeded the placebo scores by more than 20% (23.8 and 0.2% for probiotics and placebo, respectively, P = 0.003). There was a significant difference in the proportion of responders between the probiotics and placebo groups (P = 0.011). There was no drop out or adverse events for either group during the study period. Lactobacillus acidophilus-SDC 2012, 2013 appeared to have a beneficial effect in patients with IBS. Further studies are warranted.