This study evaluates the production capacity of multi-layer composite materials from Sargassum algae reinforced with coconut leaf sheaths and bonded with polylactic acid resin. Dried Sargassum seaweed, with a particle size of more than 0.4 mm and less than 2 mm, was mixed with polylactic acid (PLA) and hand-molded into simple panels. The coconut leaf sheaths were then interposed between the PLA/Sargassum panels to produce multilayer composites by hot pressing. The composite materials were tested for flexural strength, density, porosity and biodegradability. The results show that increasing the molding pressure significantly improves the bulk density and flexural strength of composite materials produced with 10% by weight of PLA. In addition, the flexural strength obtained by introducing one layer of coconut leaf sheets was between 3.3 and 14.77 MPa, while introducing three layers of coir sheets was between 3.92 and 19.02 MPa. The coconut leaf sheaths act as anti-cracking agents, while improving the toughness of the composite. In addition, the average bulk density of the composites is less than 1000 kg/m3 and classified as medium density panels, while their porosity is between 23.73 and 50.99%. The weight loss after the biodegradation test ranged from 8.33 to 66.22% by weight, with the highest biodegradation observed on the composite consisting of a single layer of leaf sheaths. Although the multi-layers composite has acceptable mechanical performance, appropriate treatment should be applied to the Sargassum algae to control its water resistance.