Because the control of parasitic nematodes of livestock mainly relies on anthelmintics, the development of resistance represents a major concern. In this context, the bioactive compounds from macro-algae and their putative anthelmintic and/or biostimulant properties offer attractive perspectives for the development of alternatives to control strategies. In the present study, we have investigated the potential anthelmintic activity of aqueous extracts from a panel of seaweeds collected in Brittany coast of France. The anthelmintic activity of the algae was determined on the murine parasite Heligmosomoides polygyrus bakeri, via several in vitro tests. A larval development test, consisting of measuring the ability of the algae extracts to inhibit the development of larvae from the L1/L2 to the L3 stage, was used to screen the different extracts. Some extracts completely inhibited larval development at 5g/L . The IC50 value of the most efficient extract was 0.7g/L. Strikingly, this extract, derived from brown seaweed also inhibited egg hatching and has a strong nematicidal activity on post-hatching larvae. Moreover, we report a high efficacy of this extract on adult worms. As a next step, fractionation of the aqueous extracts will be performed in order to identify the active compounds, and in vivo tests on infected mice will be used to further validate this macro-algae extract as a potential natural anthelmintic.