The giant diatom Coscinodiscus wailesii is one of the harmful species for Nori (Porphyra) culture from autumn to spring in the Harima-Nada, eastern part of Seto Inland Sea, Japan. The growth response of C. wailesii isolated from Harima-Nada was examined on four strains in 36 different combinations of temperature (5-30°C) and salinity (10-35) under a 130 μmol m−2 s−1 and 16 h: 8 h LD photo cycle. The growth of C. wailesii was observed in most of the combinations examined and the maximum growth rate averaged for the four strains was 1.02 divisions d−1. The optimum temperature and salinity were 20-25°C and 20-30, respectively. The range of optimum temperature is in good accordance with the field data of water temperature in Harima-Nada during the period from October to November, when the autumn bloom of C. wailesii occurs. However, the growth rate at 5 to 10°C decreased more than half the maximum growth rate. Therefore, the low water temperature in Harima-Nada during the period from February to March is presumed to be one of the limiting factors that control the spring bloom of C. wailesii.