||In the present study, four different plant species were studied for their organic constituents. All the plant species were extracted and purified by chromatographic separation using a combination of methods. Each compound isolated was fully characterized by spectroscopic and physical data. NMR results (one-dimensional and two-dimensional) were carefully analysed and compared with literature data. A number of new chemical structures were found, in addition to known constituents. The investigation of an acetone extract prepared from the aerial parts of Salvia yosgadensis led to the isolation of twenty organic constituents. Of these, seven were newly reported structures. They were 6α-hydroxyambreinolide, 6α-hydroxynorambreinolide, 6α-hydroxy-8α-acetoxy-13,14,15,16-tetranorlabdan-12-oic acid, yosgadensonol, 13-epi-yosgadensonol, yosgadensolide A and yosgadensolide B. Nine organic constituents were isolated and identified from an ethanol extract prepared from the roots of Stephania sutchuenensis. These constituents were identified as aknadinine, 1-nitroaknadinine, sinococuline, liriodenine, thalrugosine, pronuciferine, β-sitosterol, pentadecanoic acid ethyl ester and palmitic acid ethyl ester. Aknadinine is a rare hasubanan alkaloid, and 1-nitroaknadinine is a new natural analogue which is now reported for the first time of its occurrence in plants. An acetone extract of Rabdosia ternifolia was purified by column chromatography and recrystallization to afford an unsaturated lactone, 1O-epi-olguine. The structure was established by spectroscopic means, especially 2D-NMR and X-ray crystallographic analyses. Four organic constituents were isolated from a methanol extract prepared from the twig part of Erythrina rubrinewia by repeated chromatography. These constituents were identified as coumestrol, daidzein, stigmasterol and octacosan-l-o1. Selected organic constituents were subjected to different biological assays and several showed promising results. Hence these new compounds deserve further testing for other biological activities and as lead compounds for synthetic modification.