Hypericum quartinianum A. Rich. (Hypericaceae) is a shrub or small tree occurring in East Africa and used in African traditional medicine against diarrhea and fungal infections. This study reports the first chemical investigation of H. quartinianum. Air-dried and powdered leaves were successively extracted with chloroform and methanol, followed by chromatographic separation (silica gel, Sephadex LH-20, RP18 HPLC) and spectroscopic analysis (NMR, HRMS). Five compounds were isolated and identified: two hydroxylated fatty acids [(10E,12Z,15Z)-9-hydroxy-10,12,15-octadecatrienoic acid (1) and (10E,12Z)-9-hydroxy-10,12-octadecadienoic acid (2)], shikimic acid (3), quercetin (4), and β-sitosterol (5). Compounds 1 and 2 are reported for the first time from the genus Hypericum. Shikimic acid (3) and quercetin (4), characteristic of the subfamily Hypericoideae, support the chemotaxonomic significance of Hypericaceae as a separate family. Shikimic acid (3) is a major component of H. quartinianum, representing a new natural source of this bioactive compound. The results contribute to the chemotaxonomic knowledge of African Hypericum species, reveal interspecies chemovariability, and support the relationship between H. quartinianum and other Hypericum species.