Reactive oxygen and nitrogen species-mediated cellular aging has been linked to diseases such as atherothrombosis and cancer. Although pentraxin 3 (PTX3) is associated with aging-related diseases via TLR4-dependent anti-inflammatory effects, its relationship with oxidative stress in aging remains to be elucidated. Exercise is proposed as the key intervention for health maintenance in the elderly. This study aimed to examine the association of PTX3 levels with changes in oxidative stress in both plasma and peripheral blood mononuclear cells (PBMCs), following aerobic training in elderly adults. Nine trained and five controls participated in an eight-week aerobic training protocol. Enzyme-linked immunosorbent assay (ELISA) and Western blot analyses were used to determine PTX3, toll-like receptor 4 (TLR4), and levels of oxidative stress biomarkers [3-nitrotyrosine (3NT), 4-hydroxynonenal (4-HNE), reduced glutathione (GSH), protein carbonyl (PC), reactive oxygen/ nitrogen species (ROS/RNS), trolox equivalent antioxidant capacity (TEAC)] in plasma and/or PBMCs. Results showed a down-regulation of PTX3 expression in PBMCs following aerobic training, along with decreased PTX3/TLR4 ratios. Oxidative stress responses in PBMCs remained unchanged with the exercise protocol. Comparable levels of plasma PTX3 and oxidative stress biomarkers were observed in trained vs. control groups. No correlation was found between PTX3 and any oxidative stress biomarkers following training. These findings demonstrated the down-regulation of PTX3 and PTX3/TLR4 ratio, irrespective of oxidative stress response, in elderly adults following eight weeks of aerobic training.