The use of seaweed as feed ingredient is gaining interest but the high ash content, low nutrient digestibility, short shelf life and poor economic feasibility hamper practical application. This study investigates the effect of washing, ensiling and extraction processes on the nutritional value of seaweed products for broilers, based on nutrient content and in vitro and in vivo digestibility. The effects of ensiling, washing and extraction processes were evaluated using Saccharina latissima, Laminaria digitata and Ulva lactuca, with 2, 4, and 6 h incubations in an in vitro simulated digestibility model, to obtain insight into the kinetics of digestibility. In an in vivo study, 160 Ross 308 male broilers were fed (day 14–22) a basal grower diet, or the basal grower diet with 100 g/kg of S. latissima silage or silage residue. Performance and ileal and total tract nutrient digestibility were determined. Washing and ensiling reduced the ash content, but also the in vitro organic matter digestibility (both P < 0.001). Washing also reduced nitrogen digestibility (P < 0.001). Extraction of seaweed decreased in vitro organic matter and nitrogen digestibility. Feeding seaweed diets to broilers resulted in a higher feed conversion ratio (1.62 versus 1.86 and 1.77 for broilers fed the basal, silage and silage residue diets respectively, P < 0.001) without increase in final body weight. Feeding S. latissima silage residue compared to silage resulted in a slightly better broiler performance and a higher amino acid digestibility. In conclusion, washing, ensiling and extraction processes reduce the nutritional value of the seaweed products, and do not make seaweed suitable for inclusion in broiler diets. To create suitable seaweed products for inclusion in broiler diets, a further reduction in the ash content and increase in digestibility is needed.