Bifidobacteria species were incubated anaerobically with daidzein in Brain Heart Infusion broth at 37 °C for 96 h. Equol production started during the first 6 h incubation with Bifidobacterium breve ATCC 15700 (B. breve) and Bifidobacterium longum BB536 (B. longum). The pH decreased during incubation of the bacteria with daidzein more than that in its absence. However, there was no significant difference in the growth of bifidobacteria strains when incubated in the culture medium with or without daidzein. The production of lactic and acetic acids after 96 h incubation with daidzein for B. breve was 5.53 and 8.83 mmol l−1, respectively, while for B. longum was 6.86 and 7.20 mmol l−1, respectively. Thus, probiotic bacteria were able to produce equol from daidzein, hence dietary supplementation with equol may offer an important approach to provide all consumers with the health-promoting benefits of this metabolite.