BACKGROUND: Prematurely aged mice (PAM), characterized by an inadequate stress response, exhibit early immunosenescence and reduced lifespan compared with exceptional non-PAM (E-NPAM) of the same age. Lacticaseibacillus rhamnosus GG (LGG) has been proposed as a beneficial probiotic in healthy aging. This study aimed to evaluate the effects of LGG consumption over 2 and 4 weeks on behavioral parameters, peritoneal leukocyte function, and lifespan in adult female PAM. RESULTS: Female ICR-CD1 mice were classified as either PAM or E-NPAM and divided into three groups: (1) PAM control (PAMC), (2) PAM receiving LGG (PAMLGG), and (3) E-NPAM control (E-NPAMC). The PAMLGG group consumed a lyophilized LGG suspension in skim milk for 4 weeks, while the PAMC and E-NPAMC groups received a skim milk solution. Behavioral tests were conducted after 2 weeks, and leukocyte function was analyzed after 2 and 4 weeks. The results showed that the PAMLGG group exhibited improved behavioral responses and enhanced immune functions, which was reflected in a lower biological age and in a longer longevity compared with the PAMC. CONCLUSION: LGG supplementation positively influenced behavior, immune function, and biological age markers in female PAM, leading to increased longevity. These findings indicate that LGG administration could be a good nutritional strategy for slowing down the aging process, allowing a healthy longevity to be achieved. © 2025 Society of Chemical Industry.