Rhodiola rosea L. (Crassulaceae), the most investigated species of the genus Rhodiola, grows at elevated altitudes in the Arctic and in mountainous regions throughout Europe and Asia, where it is also knows as "Golden root" or "Arctic root". The roots have been used for centuries in traditional medicine to enhance physical and mental performance, improve resistance to high altitude sickness and to treat fatigue, psychological stress and depression. The present work aims at clarifying the pharmacological effects of R. rosea and identifying the active metabolites. The plant was tested on three targets : monoamine oxidase, acetylcholinesterase and oxidative stress. As the roots of R. rosea exhibited interesting activities against the three targets, a phytochemical investigation was undertaken on the plant. An agronomical study was also realised on R. rosea. Another part of this work consisted in studying different Crassulaceae species in order to discover new potential herbal stress buster. Six new flavonols were isolated from Sedum dasyphyllum L.