Protein NP24 found in tomato (Solanum lycopersicum L.) and PR5-like protein in sweet pepper (Capsicum annuum L.) are homologous proteins of osmotin. Osmotin is known to show adiponectin-like activity, and therefore, protein NP24 and PR5-like protein are expected to show similar activity. In this study, we quantified these proteins contained in the fruits of tomato and sweet pepper cultivars using protein absolute quantification (AQUA) technology employing liquid chromatography/tandem mass spectrometry (LC/MS/MS) and stable isotope-labeled internal standard peptide,GQTWVINAPR[13C6,15N4] (AQUA peptide). The range and average of protein NP24 content in 12 tomato cultivars were 0.43+-0.040 (‘Reika’) to 0.83+-0.40 (' Momotaro Fight' ) and 0.66+-0.14 nmol/g fresh weight, respectively. The PR5-like protein content in 5 sweet pepper cultivars ranged from 0.079+-0.034 ('Ferrari’ harvested in September) to 0.54+- 0.14('Helsinki' harvested in December) nmol/g fresh weight. This study could contribute to research on the application of these proteins as adiponectin agonists and the use of tomato and sweet pepper as functional foods.