Genomic library with highmolecular weight inserts is an essential and powerful tool for genomic studies. An unbiased fosmid library of Porphyra yezoensis was constructed and characterized. The library comprised 23 040 clones with 100％ recombination frequency. The range of insert size of most bulk of clones is from 28 kb to 40 kb and the average size is about 35 kb. Therefore, the library coverage is about 2.78 genomeequivalent. The theoretical coverage was verified by successfully screening out 4 randomly selected genes, 18S rRNA, atpA, h2A and rbcL, once at least from the super pools which covered the whole library clones. No variations were observed by comparing the original clones with those of the hundredth generation cultivated successively, indicating the good fidelity and stability of the fosmid library. This study laid the foundations for gene cloning and genomic research in P. yezoensis.