We investigated the water temperature characteristics in growth of filamentous thallus and formations of spherical cell, uniseriate and foliose thallus of Pyropia tenuipedalis with culture experiments. Optimal growth of filamentous thalli was observed at 20℃. Moreover, optimal water temperatures in formations of spherical cells, uniseriate and foliose thalli were 20ºC, 15-20ºC and 15ºC., respectively. Optimal water temperatures of each life stage were different. At 10ºC, the formations to uniseriate and foliose thalli were suppressed. At 25ºC, almost of all thalli has caused morphological abnormalities. Furthermore, changing to 15ºC from 20ºC was promoted for forming to uniseriate and foliose thalli. It was thought that bad harvest in 2012 was resulted from suppressing of formation to uniseriate and foliose thalli at the condition of less than 10ºC. The present results are able to contribute for improvement of the seedlings production techniques in P. tenuipedalis mariculture, and prediction of the development time of the mariculture plates in the waters.