Phytochemical compositions of five varieties of black soybeans (Glycine max) and their stabilities at room temperature, 4 and −80°C over 14months were determined by HPLC systems with electrochemical (ECD) and UV detectors. Polyphenol profiling was carried out by a liquid chromatography–electrospray ionisation-mass spectrometry (LC–ESI-MS) with orbitrap as a mass analyser in both positive and negative ion modes, and polyphenols in aglycone forms were quantified by HPLC–ECD. Five different varieties of black soybeans (G. max) contained 249–405μg/g dry wt of γ-tocopherol and 6.76–14.98μg/g dry wt of lutein. Major polyphenols in black soybeans (G. max) were daidzein (193–288μg/g dry wt) and genistein (145–223μg/g dry wt), mainly present as glucosides and acetyl glucosides. No significant decrease was found in total phenols of black soybeans (G. max) stored at room temperature, 4 or −80°C for 14months. On the other hand, lutein and γ-tocopherol degraded significantly within a month of storage at room temperature (p