Abstract: Multiple banding pattern, a potential problem of cross-species microsatellite amplilification, happened when EST-SSR primers of Porphyra yezoensis were used in microsatellite amplification for several lines of Porphyra haitanensis. These PCR products were sequenced to identify false positive amplification. Among the recovered productsfrom P. haitanensis., bands with simlar size to the amplification product of positive control from P. yezoensis contained the anticipated SSR. Sequence alignment showed high identity. The microsatellite signature was absent from the amplification products with bigger molecular weight. This result showed a typical false positive problem. Therefore primersthat producedfalse positive products in P. haitanensis can not be used in those genetic analyses based onmodels of SSR mutation, such as the diploid conchocelia pure line test of P. haitanensis.However, they are still useful for the species identification and other genetic researches.