Turkey is an important center in terms of Hypericum species and 49 of the 119 taxa are endemic. Hypericum heterophyllum is one of these endemics. This study was carried out in order to determine some chemical properties of H. heterophyllum. In dry capsules, 14% protein and 23% oil were detected. This oil has been found to be rich in unsaturated fatty acids (oleic and linoleic). The highest essential oil rate (0.09%) in flowering dry herb was recorded in the period before flowering. Also, germacrene-D, bicyclogermacrene, δ-cadinene, spathulenol, α-guaiene, and valencene in herbage essential oil and limonene, cis-ocimene, β-myrcene, and α, β-pinene in dry capsule were determined as main components. It has been noted that both the essential oil content and the components show variation depending on the developmental stages of the plant and the part used.