Seedstring cultivation is a fundamental method for Pyropia yezoensis aquaculture, as it provides an artificial substrate for the attachment of P. yezoensis conchospores and growth of the macroscopic blade gametophytes. This method has been widely used in the P. yezoensis aquaculture in Asia due to its convenience for Pyropia management and harvest. However, the composition and types of seedstrings vary in different countries. Little is known about the effect of different seedstrings in terms of spore attachment and early development of the gametophytes in P. yezoensis . In this study, four types of commercially available seedstrings from Korea (KR), China (CN) and Japan (JP1 and 2) and three new seedstring types developed by W.L. Gore & Associates Inc. (Gore A, B and C) were compared. The comparisons were conducted in three aspects: seeding density, growth rate and biomass yield. Our results show that, for both conchospore and archeospore seeding, the Gore C seedstring had the highest seeding density and yield among all seedstrings while the Gore B had the lowest. For conchospore seeding, the Gore A and B seedstrings had the highest growth rate at the early stages of gametophytes too. In the case of archeospore seeding, the difference between Gore A and other seedstrings was not significant. The CN and KR seedstring showed lower growth rates than the other seedstring types in the case of conchospore seeding. A comprehensive evaluation shows that the Gore C seedstring type, had the best performance among all seven seedstrings under laboratory conditions (Fig. 1) . Future studies are needed to test the performance of the seedstrings on Pyropia farms