Various species of the genus Digitalis have been used as a source of cardiac glycosides which are important for their use in medicine. Progesterone 5β-reductase (P5βR) plays a key role in the biosynthesis of β-cardenolides of Digitalis. In this research, progesterone 5β-reductase gene expression was determinated in Digitalis trojana Ivanina, an endemic plant of Kazdagi Mountain (Mt. Ida), Turkey. The expression of progesterone 5β-reductase gene was showed variations in the plants which were collected in different seasons and altitudes. The minimum and maximum gene expression profiles were calculated respectively in 836 m and 1191 m altitudes in May. Minimum and maximum gene expression levels were calculated respectively in 1191 m and 1047 m altitudes in July.