We report the unique self-catalyzing chemiluminescence (CL) of luminol-diazonium ion (N2+-luminol) and its analytical potential. Visual CL emission was initially observed when N2+-luminol was subjected to alkaline aqueous H2O2 without the aid of any catalysts. Further experimental investigations found peroxidase-like activity of N2+-luminol on the cleavage of H2O2 into OH• radical. Together with other experimental evidence, the CL mechanism is suggested as the activation of N2+-luminol and its dediazotization product 3-hydroxyl luminol by OH• radical into corresponding intermediate radicals, and then further oxidation to excited-state 3-N2+-phthalic acid and 3-hydroxyphthalic acid, which finally produce 415 nm CL. The self-catalyzing CL of N2+-luminol provides us an opportunity to achieve the attractive catalyst-free CL detection of H2O2. Experiments demonstrated the 10-8 M level detection sensitivity to H2O2 as well as to glucose or uric acid if presubjected to glucose oxidase or uricase. With the exampled determination of serum glucose and uric acid, N2+-luminol shows its analytical potential for other analytes linking the production or consumption of H2O2. Under physiological condition, N2+-luminol exhibits highly selective and sensitive CL toward 1O2 among the common reactive oxygen species. This capacity supports the significant application of N2+-luminol for detecting 1O2 in live animals. By imaging the arthritis in LEW rats, N2+-luminol CL is demonstrated as a potential tool for mapping the inflammation-relevant biological events in a live body.