While searching for lactic acid bacteria that can restore aging-impaired immune responses, we isolated the Toll-like receptor (TLR) 2/NF-kappaB-activating strain Lactobacillus plantarum HY7712 from kimchi and investigated its immunomodulating effect in whole-body γ-irradiated mice. Exposure to HY7712 strongly activated NF-kappaB signaling in RAW264.7 cells, but inhibited lipopolysaccharide-stimulated NF-kappaB activation. Moreover, HY7712 protected against the downregulation of interferon (IFN)-γ and upregulation of interleukin (IL)-13 caused by γ-irradiation in mice. In mice, γ-irradiation impaired NK-cell activity against YAC-1 tumor cells, but following HY7712 exposure, the activity of NK cells was restored to 91.5% of the level measured in control mice (p < 0.05). These findings suggest that HY7712 activates the TLR2/NF-kappaB signaling pathway and protects against the impairment of NK-cell activity caused by γ-irradiation or aging.