The anthelmintic activity of Citrus sinensis fruit juice on eggs, first stage larvae (L1) and adults of Heligmosomoides bakeri was examined by in vitro and in vivo tests. Freshly harvested C. sinensis fruit was washed and sliced into two halves each, which were squeezed gently into a clean container to obtain the juice after filteration through a Whatsman paper. The fruit juice was prepared to obtain seven increasing concentrations. Distilled water and albendazole were used as negative and positive control groups, respectively. At the concentrations of 0.01, 0.02, 0.03, 0.04, 0.05, 0.5 and 1.0 mg/ml the fruit juice inhibited the hatching of eggs by 11.4±2.77, 11.90±3.61, 14.03±2.72, 18.67±2.0, 24.93±2.06, 89.60±1.80 and 100±0.0 %, and killed the larvae by 34.70±5.74, 48.35±1.65, 65.97±6.28, 78.55±1.45, 87.85±2.15 and 97.77±2.23 %, respectively. The plant caused a significant (P<0.05) deparasitization rate of 74.6 % of the adult worms at the dose of 800 mg/kg per os in mice. This study demonstrates that Citrus sinensis fruit juice possess anthelmintic activity.