Abstract: This study analyzed the external morphology, vegetative and reproductive structure, growth process, biomass variation, mature individual proportion, R/T index, as well as the large subunit of ribulose-1, 5-bisphosphate carboxylase/oxygenase (rbcL) gene and the partial cytochrome coxidase Ⅰ (COⅠ) gene sequences of Gloiosiphonia capillaris (Hudson) Carmichael populations collected in the coast of Heishijiao, Fujiazhuang, Shicao, Jinshitan, Zhangzidao and Haiyangdao in Dalian. The results indicated that the gametophytes of G. capillaris were androgynous, solitary or caespitose habit, and that the main axes were erect, disciformi affixus, gelatinous in texture, red or purplish red. The length and width of thallus collected in Zhangzidao and Haiyangdao were significantly higher than those in other sites. Thallus was composed of cortex that had 6—10 cell layers and medulla that was consisted of many rhizoidal filaments. The size of mature cystocarp was small and protruded from the thallus. Cystocarps were spherical or hemispherical, and often became a group with 2—4 members. The maximum biomass of gametophyte appeared in June with an average value of 3.628 g/m². The proportions of mature individuals increased gradually from March to June and got 100% in June. The gametophyte growth cycle was from March to July, and the temperature property was temperate. According to the phylogenetic tree of rbcL gene sequences, there was no sequence divergence among the 6 sites and clustered in a single monophyletic subclade with the sample from Canada. There was also no sequence divergence among the 6 sites based on the phylogenetic tree of COⅠ gene sequences. The samples were clustered in a single monophyletic subclade and identified as G. capillaris.