Journal of Medicinal Plants Research 2013, 7(14): 863-870.Investigation on the effect of root bark and wood, stem bark and wood, leaves and sap of Synadenium glaucescens extracts against Newcastle disease (ND) virus was done using an in ovo assay. Viable 9 days embryonated chicken eggs were arranged into 25 treatment groups (n = 5). Groups 1 to 21 were challenged with a 13C/SUA virulent strain of ND virus treated with extract at concentration of 0.2 mg/ml. Un-inoculated group saved as negative control and groups inoculated with virus and diluent saved as positive controls. Haemagglutination test was used to quantify the amount for ND virus units. Embryo survival and embryo weight were significantly higher (P ≤ 0.05) in groups treated with S. glaucescens extracts than the positive control. The root bark demonstrated significantly higher antiviral activities (P ≤ 0.05). Furthermore, treatments with ethanolic extract SE1 resulted into 100% embryo survival, 91.2% mean embryo weight and reduced viral load by 99.2%. The minimum dose of SE1 with the highest efficacy was 0.2 mg/ml. The percent mean embryo weight and haemagglutination test demonstrated negative correlation (R2 = 0.94). These findings validate the ethnoveterinary potential of S. glaucescens and the feasibility of its use for treatment and control of ND.