This study compared relative growth rates (RGRs) of Neopyropia yezoensis and Neopyropia dentata in response to changes in water temperature (20, 22, 24, 26 and 28°C) and light intensity (40 and 80 μmol m-2·s-1) during early growth stages (1 and 10 mm). After 2 weeks of cultivation under a combination of high temperature and light intensity, the limit growth condition was 22°C for N. yezoensis and 26°C for N. dentata. N. yezoensis with 1 mm blade crimpled seriously at 22 to 26°C than its 10 mm blade. Both sizes were completely dead at temperature over 26°C. On the other hand, N. dentata was able to grow at relatively high temperatures. It grew higher with 10 mm blade than with 1 mm blade. N. dentata showed a normal color and displayed a flat surface without any decay at 28°C. The growth of N. dentata was limited and crimpled at 26 and 28°C 40 μmol photons m-2·s-1 conditions, although its normal growth and morphology were observed under other conditions. In the case of light intensity, it was confirmed that 80 μmol photons m-2·s-1 was more appropriate for grow of both species than 40 μmol m-2·s-1.