<p>Native populations of <i>Undaria pinnatifida</i> in China are historically recorded to be distributed in Zhejiang and Fujian provinces, whereas the natural populations on the rocky coasts of northern China are documented to have originated from Korea. Given the suitability of the coastal environment for the growth of <i>U. pinnatifida</i>, whether there are native populations existing in northern China remains uncertain. Although no novel haplotypes were found in natural specimens collected from rocky shores of Dalian and Qingdao in our previous studies, samples from the only three sites may not be sufficiently extensive. Genetic diversity and population structure of <i>U. pinnatifida</i> in this region could be more complex than understood. In this study, seven natural populations were sampled from the rocky coasts of Shandong Peninsula and analyzed using informative mitochondrial sequences. By utilizing the combined <i>cox3</i> and <i>tatC-tLeu</i> sequences, no unique haplotypes were detected and all haplotypes identified from these seven populations belonged to the Continental type. Together with the results in our previous studies, it was further confirmed that there was no native <i>U. pinnatifida</i> population found in northern China and the existing populations originated from Korea. The natural populations from Shandong Peninsula exhibited high genetic diversity except for that from Qingdao. This study complements the previous population genetic studies of <i>U. pinnatifida</i> in China, providing a deeper understanding of their origin and current genetic diversity and population structure.</p>