Objective: To determine any relationship between temperaments of medicinal plants referred to traditional Iranian manuscripts and their major chemical compounds.
Methods: Plants used in traditional Iranian medicine were categorized based on their major chemical compounds including alkaloids, phenolic compounds, and essential oils. Their temperaments were extracted from traditional herbal pharmacopeias of Iran. The possible relationship between major chemical compounds and temperaments of each group were evaluated.

Results: Plants containing phenolic compounds as their major constituents are hot and dry temperaments except those contain tannins with cold and dry temperaments. Plants containing essential oils have hot and dry temperaments except those whose major essential oils with alcoholic structure which have cold and dry temperaments. Alkaloid-containing plants have cold and dry or hot and dry temperaments based on their alkaloidal structures.

Conclusions: There is a close relationship between major chemical compounds of medicinal plants and their temperaments mentioned in traditional Iranian manuscripts.

Keywords: traditional Iranian medicine; temperament; alkaloids; phenolic compounds; volatile oils