Growth and reproduction of Porphyra kuniedae from the southern coast of Korea were investigated. Biomass, plant size and occurrence of reproductive structures were monitored every other week from November 2001 to March 2002. Release of zygotospores and monospores from the plants was induced and the number of spores was counted in the laboratory culture every month. Biomass and plant size were found to be inversely correlated with water temperature. The maximum values in biomass and plant size were observed in mid-January with the lowest water temperature, and the values decreased with the increase of water temperature. Based on the cohort analysis, three cohorts started in late November, one to two cohorts were added every other week, and the maximum was eight in mid-January. The percentage of matured plants in the field was the highest in January. In the laboratory culture test, zygotospores were released more than monospores from large plants in late December while monospores were released much more than zygotospores since late January.