Life history of Porphyra variegata (Kjellman) Kjellman was completed in culture from Ken-nich, Hokkaido, Japan. Growth and reproduction of both foliose phase and conchocelis phase were observed at various temperatures (5, 10, 15, 20, and 25°C) with a photon flux density of 40 μmol·m−2s−1 under photoperiods (14L : 10D and 10L : 14D). The optimum growth of the conchocelis filaments occurred at 10°C. Conchocelis filaments produced conchosporangial branches after 6-9 weeks at 5°C and 10°C under a short photoperiod of 10L : 14D. Conchospores were released in great nombers from the conchosporangia at 10°C under short photoperiods of 10L : 14D and 8L : 16D. Conchospore germlings developed into the foliose thallus and reached to 1-5 cm in length after 3-5 months at 5°C and 10°C under long and short photoperiods. The foliose thallus produced only sexual spores as zygotospores. Reproductive organs were not produced from small globular thalli at 15°C. Asexual spores were not produced from the foliose thallus.