Using plants and their metabolites is a valuable strategy to tackle parasitic infections by gastrointestinal nematodes (GIN) in integrated control strategies aiming at reducing dependence on synthetic drugs. Several salt tolerant plants (halophytes) have ethnoveterinary uses as antiparasitic, and are rich in bioactive molecules (e.g., tannins), and are therefore potential sources of anthelminthic phytotherapeutic products. This work explored the tannins content and the in vitro athlelminthic properties towards eggs and larvae of Haemonchus contortus and Trichostrongylus colubriformis of acetone extracts made from aerial organs of halophytes common in the Mediterranean, namely Pistacia lentiscus L., Cladium mariscus (L.) Pohl, Inula crithmoides L., Helichrysum italicum (Roth) G. Don subsp. picardi (Boiss. & Reut.) Franco, Calystegia soldanella (L.) R. Br., Medicago marina L., Plantago coronopus L., Limoniastrum monopetalum (L.) Boiss. and Crucianella maritima L. Cladium mariscus was one of the active in both GIN and life stages, it inhibited larvae exsheathment (IC50 ranging from 77.8 – 88.9 µg/mL), without differences between both parasite species, and was more effective towards eggs H. contortus (IC50= 496.6 µg/mL) than T. colubriformis (IC50=2575.5 µg/mL−1). The main compounds identified in the C. mariscus extract, by HPLC-ESI-MSn analysis, were flavan-3-ols (epigallocatechin, catechin), proanthocyanidins, luteolin, C-glycosyl luteolin, a kaempferol glucoside, and an apigenin flavone, the majority with recognized anthelmintic effects.