The emergence and spread of resistance to chemical anthelmintics in gastrointestinal nematode populations has led to the search for alternative solutions such as the use of medicinal plants with anthelmintic properties. This study was undertaken to examine the in vivo effect of Parkia biglobosa and Pterocarpus erinaceus on the viability and fertility of adult Haemonchus contortus worms in sheep. Fifteen Djallonke sheep, ۴ to ۵ months old, were divided into three experimental lots. The control lot received no treatment. Two lots were treated with ۳.۲ g/kg PV of plant powder. P. biglobosa significantly reduced egg excretion compared to the control (p < ۰.۰۵). Both plants significantly (p < ۰.۰۵) reduced the number of adult worms and the number of eggs per female worm. Numbers of adult worms and eggs per female worm were ۳۳۰.۰۰ ± ۱۱۲.۸۴ and ۳۳۲.۰ ± ۱۹۱.۹ in the control lot, ۱۷.۵۰ ± ۱۰.۴۱ and ۱۷۶.۰ ± ۹۶.۱ in the lot treated with P. biglobosa and ۸۶.۲۵ ± ۵۳.۱۳ and ۱۴۶.۸ ± ۹۰.۶ in the lot treated with P. erinaceus, respectively. This study showed that P. biglobosa and P. erinaceus exerted anthelmintic activity in vivo on adult H. contortus worms. Further investigations are needed to evaluate the toxicity of these plants and to understand their metabolism in the digestive tract of animals.The emergence and spread of resistance to chemical anthelmintics in gastrointestinal nematode populations has led to the search for alternative solutions such as the use of medicinal plants with anthelmintic properties. This study was undertaken to examine the in vivo effect of Parkia biglobosa and Pterocarpus erinaceus on the viability and fertility of adult Haemonchus contortus worms in sheep. Fifteen Djallonke sheep, ۴ to ۵ months old, were divided into three experimental lots. The control lot received no treatment. Two lots were treated with ۳.۲ g/kg PV of plant powder. P. biglobosa significantly reduced egg excretion compared to the control (p < ۰.۰۵). Both plants significantly (p < ۰.۰۵) reduced the number of adult worms and the number of eggs per female worm. Numbers of adult worms and eggs per female worm were ۳۳۰.۰۰ ± ۱۱۲.۸۴ and ۳۳۲.۰ ± ۱۹۱.۹ in the control lot, ۱۷.۵۰ ± ۱۰.۴۱ and ۱۷۶.۰ ± ۹۶.۱ in the lot treated with P. biglobosa and ۸۶.۲۵ ± ۵۳.۱۳ and ۱۴۶.۸ ± ۹۰.۶ in the lot treated with P. erinaceus, respectively. This study showed that P. biglobosa and P. erinaceus exerted anthelmintic activity in vivo on adult H. contortus worms. Further investigations are needed to evaluate the toxicity of these plants and to understand their metabolism in the digestive tract of animals.