Abstract : <p>Treatment for sex hormone depletion along with chronic inflammation would be beneficial for aging males. Mesenchymal stem cells (MSC) are known for their immunomodulatory activities and differentiation ability in regenerative medicine. Whether MSC could influence both testosterone and pro-inflammatory marker in aging males is uncertain. This study aimed to explore the effects of human umbilical mesenchymal stem cell (hUCMSC) on testosterone, tumor necrosis factor-alpha (TNF-&alpha;), and creatinine levels in aged rats. The hUCMSC was administered to aged male Sprague-Dawley rats (24 months old). After four injections of 1 million per kg body weight in 3-month intervals, the rats were sacrificed, and serum was collected for biochemical examinations. The hUCMSC administrations increased the testosterone level almost three-fold and decreased the TNF-&alpha; level. Moreover, the high testosterone level was strongly correlated with low TNF-&alpha; level (p = 0.013; r = -0.863) in aged male rats. These results were following our previous report, which showed that the hUCMSC increased the number of Leydig cells. Serum creatinine levels in the treatment group were slightly increased but were still within the normal limit. The hUCMSC treatment in aged male rats tends to increase testosterone levels and lower TNF-&alpha; levels.</p>