AbstractAging is the primary risk factor for the development of numerous human chronic diseases. On a molecular level, it significantly impacts the regulation of protein modifications, leading to the accumulation of degenerative protein modifications (DPMs) such as aberrant serine phosphorylation (p‐Ser) and trioxidized cysteine (t‐Cys) within the proteome. The altered p‐Ser is linked to abnormal cell signaling, while the accumulation of t‐Cys is associated with chronic diseases induced by oxidative stress. Despite this, the potential cross‐effects and functional interplay between these two critical molecular factors of aging remain undisclosed. This study analyzes the aging proteome of wild‐type C57BL/6NTac mice over 2 years using advanced proteomics and bioinformatics. Our objective is to provide a comprehensive analysis of how t‐Cys affects cell signaling and protein structure in the aging process. The results obtained indicate that t‐Cys residues accumulate in the aging proteome, interact with p‐Ser interacting enzymes, as validated in vitro, and alter their structures similarly to p‐Ser. These findings have significant implications for understanding the interplay of oxidative stress and phosphorylation in the aging process. Additionally, they open new venues for further research on the role(s) of these protein modifications in various human chronic diseases and aging, wherein exacerbated oxidation and aberrant phosphorylation are implicated.