Eight Phaseolus vulgaris L. landraces cultivated on farm in marginal areas of Central Italy (Lazio region) were investigated in order to evaluate chemical composition of storage proteins and secondary metabolites fractions. The total protein content showed some differences among landraces; the maximum value was next to 30 g for 100 g of dry weight. The seed storage proteins were screened by polyacrylamide gel electrophoresis (SDS/PAGE): seven landraces exhibited phaseolin patterns type S, one landrace showed a phaseolin pattern type T. A morphological analysis of cotyledon parenchyma performed by scanning electron microscopy (SEM) revealed differences in size of starch granules. Moreover the polyphenolic composition was investigated using HPLC-APCI; from the methanol extracts a flavonoid, kaempferol, and a coumarin, 5,7-dimethoxycoumarin, were identified. To our knowledge, this is the first time that 5,7-dimethoxycoumarin has been reported in P. vulgaris seeds.