Hydro-distilled essential oils from leaves of Piliostigma thonningii and P. reticulatum (Caesalpiniaceae) were studied by combined gas chromatography and gas chromatography-mass spectrometry for the first time. Both qualitative and quantitative differences existed in the composition of the two oils. While P. thonningii oil is composed of sesquiterpenes and monoterpene hydrocarbons, monoterpenes and sesquiterpene hydrocarbons represented the chief class of terpenoids in P. reticulatum. Major constituents in P. reticulatum leaf oil were γ-muurolene (10.3%), α-pinene (9.4%), tricyclene (7.2%), δ-cadinene (5.6%), α-terpineol (5.3%) and β-caryophyllene (4.2%). However, the sesquiterpene-rich P. thonningii oil was characterized by β-myrcene (13.3 %), limonene (8.6%), α-pinene (7.6%), β-caryophyllene (7.1%), γ-muurolene (6.1%), caryophyllene oxide (5.2%) and spathulenol (4.0%).