Phytonutrients in Angelica keiskei, a dark green leafy vegetable, were characterised and their extraction efficiency by different compositions of water/ethanol as well as stability at different temperatures was determined. A range in the content of lutein (205–265 mg/kg dry wt), trans-β-carotene (103–130 mg/kg dry wt), and total phenols (8.6–9.7 g/kg) was observed amongst Angelica keiskei grown in three different conditions. LC-ESI-MS/MS analysis identified chlorogenic acid, chalcones and the glucosides of luteolin and quercetin as the major phenolic compounds in Angelica keiskei. Only 46% of lutein was extracted by 70% of ethanol and no carotenoid was detected in 40% ethanol and 100% water extracts of Angelica keiskei. Major phytonutrients in Angelica keiskei were stable at −80 °C up to 12 months whilst β-carotene was significantly degraded at room temperature and 4 °C within 2 months and lutein at room temperature within 12 months.The current study indicates that phytonutrients rich in Angelica keiskei can only be extracted partially using ethanol/water and substantial loss of certain phytonutrients such as β-carotene can occur during storage at either 4 °C or room temperature.