Neopyropia yezoensis is one of the most important aquaculture species in Korea. Due to global warming, it is important to develop new cultivars with thermal tolerance. Acadian Marine Plant Extract Powder (AMPEP) is known as a biostimulant, enhancing growth and resistance to temperature stresses. This study compared the growth and antioxidant activity of Neopyropia yezoensis exposed to AMPEP and Sargassum horneri extract (SHE). Blades were exposed to 1 g L-1 of AMPEP and SHE solution at 10 ? for 10 days. At the end of exposure, they were transferred to flasks with fresh medium and cultivated at 10 and 20 ? for 15 days. At 10 ?, no significant differences in terms of growth were observed. However, at 20 ?, the growth at control decreased, whereas the samples with SHE and AMPEP showed growth rates similar to those of 10 ?. The total protein contents of the SHE and AMPEP groups at 10 ? were higher than those at 20 ?, while the SHE and AMPEP groups at 20 ? showed similar results to the control group at 10 ?. These results suggest that SHE has similar effect to the commercially available seaweed derived biostimulant, AMPEP, enhancing the temperature tolerance in Neopyropia yezoensis