The measurement of total antioxidant capacity (TAC) indicating the cooperative action of all antioxidants in a complex sample is an important analytical challenge. A novel green silver nanoparticle-based antioxidant capacity (GSNP-AC) method using carob extract was designed for TAC measurement. Green synthesis of nanoparticles has various advantages such as environmentally friendliness, reliability, sustainability and fast production. In the presence of silver seeds formed with carob extract, Ag+ is reduced to spherical silver nanoparticles (SNPs) with antioxidants, resulting in enlarged particles with a symmetric surface plasmon resonance (SPR) absorption band at 434 nm. The SPR of SNPs allowed quantification of antioxidants (i.e., increase in SPR absorbance being correlated to antioxidant concentration), and the GSNP-AC method gave a linear response over a wide concentration range of antioxidants. The molar absorptivity and LOD for trolox were 11700 L mol(-1) cm(-1) and 0.31 mu M, respectively. The proposed method was validated in terms of concentration-dependent linear response, additivity of absorbances, precision and accuracy. The results obtained with the proposed method for standard antioxidants, synthetic mixtures and real sample extracts were correlated with those of the traditional CUPRAC method. This green synthesized silver nanoparticle-based TAC method showed simple, rapid, cost-effective, and eco-friendly superiorities over similar other nanoparticle-based assays.