Aging is a growing concern of age-associated aberrations in immune system or immunosenescence. Probiotics contain not only these general health advantages but also other the regulation of host immune function. Among those probiotics, the immunomodulatory effects of Weissella cibaria JW15 (JW15) strain has already been reported in our previous studies. The objective of this study is to assess improved immunity of JW15 strain in aged mice. In experiment, mice were divided into five groups. Twenty eight–month-old C57BL/6J mice were given a daily dose of 1×109 CFU/mouse (JW15-H group) and 1×108 CFU/mouse (JW15-L group) of viable JW15. The young mice group (YM) and old mice group (OM) were given PBS. After four weeks of administration, mice were euthanized. Mice blood was collected and analyzed for complete blood cell count (CBC). Then, mice spleen was weighed and analyzed for splenocyte. Finally, we measured the concentration of cytokine secreted by splenocyte and serum. The results showed splenocyte proliferation of JW15-L group by the addition of LPS and concanavalin A was significantly higher than that of OM group. Splenocyte TNF-α production was significantly increased by JW15 intake. In particular, splenocyte TNF-α production of JW15-L group by the addition of LPS (5 µg/mL) was significantly greater than that other group. Splenocyte IL-6 production was also the highest in JW15-L group. Serum IFN-γ production of JW15-L (59.13 ± 16.13 pg/mL) group was significantly higher than that of OM group (39.71 ± 2.51 pg/mL). When compared to the OM group (32.22 ± 1.92 pg/mL), Serum TNF-α production was significantly increased by JW15-H intake (69.01± 26.51 pg/mL). In conclusion, JW15 enhanced immunomodulative effects. In particular, the effect was significantly excellent in JW15-L group (1 × 108 CFU/mouse). Therefore, Weissella cibaria JW15 would be suitable for consideration as a helpful functional food for companion animals and humans.