The inclusion in the diet of biological products of a biodegradable nature is a highly valued strategy with many advantages. Posidonia oceanica is a seagrass species which may be used as a substitute for straw. In this study, one group of goats (control) was fed a normal diet that contained straw, while the straw in the diet of the other group was replaced by P. oceanica. No significant differences were found between the control and experimental group regarding the main physicochemical and sensorial parameters of the resulting milk and cheese; although the cheese from the group fed P. oceanica was firmer and chewier. When the milk-clotting time was determined under different assay conditions, the origin of the milk was found to have a significant effect, the milk from animals fed with algae showing greater technological suitability. In conclusion, P. oceanica can be used as a straw substitute, promoting a sustainable livestock system and contributing to the maintenance of meadows.