Newcastle Disease (ND) is a highly pathogenic disease of avian species which is caused by Newcastle Disease Virus (NDV). It is one of the major causes of mortality and morbidity to poultry industry in the third world countries. Currently, there is no treatment measures against ND; the only existing measure is vaccination, though it is incapable to offer 100% immunity. In Tanzania, the leaves of Synadenium glaucescens Pax. are traditionally used for treatment of various ailments including ND. Previously, its leaves extract has been scientifically confirmed to exhibit anti-NDV activity though bioactive compound(s) responsible for this activity is/are unknown. Therefore, this study was aimed to evaluate anti-NDV activity of 3β-Friedelanol (1) and 3α-friedelanol (2) isolated from its leaves extract. Isolation of these compounds was achieved by column chromatography method whereas, their chemical structures were determined by Nuclear Magnetic Resonance (NMR) data and by comparing with the available literature NMR data. Anti-NDV activity study was done in embryonated chicken eggs (ECEs). Treatment of NDV inoculated ECEs with 3β-Friedelanol (1) reduced the viral load to zero and maintained the survival of embryos, this was revealed by continuous organs formation and increase in embryo weights with no significant different (p > 0.05) from un-inoculated ECE. These effects suggest that, 3β-Friedelanol (1) possesses anti-NDV activity. Therefore, existence of 3β-Friedelanol (1) in the leaves of S. glaucescens may justify its earlier described anti-NDV activity and traditional use in the treatment of ND. Hence, its leaves extract may be considered for development of anti-NDV herbal formulation while 3β-Friedelanol could either serve as a drug or lead compound for synthesis of anti-NDV drugs.