Even though the microalgal species of Isochrysis and Pavlova are widely used as live food in bivalve hatcheries, they are difficult to culture in mass during the summer season. Therefore, the present study was conducted to determine the optimum species or strains of Isochrysis and Pavlova to produce good growth and high contents of fatty acids at temperatures over $30^{circ}C$. Four species of Isochrysis (I. galbana KMMCC12, I. galbana KMMCC214, I. aff. galbana, and Isochrysis sp.) and four of Pavlova (P. lutheri, P. gyrans, P. viridis, and Pavlova sp.) were cultured at $25^{circ}C$, $29^{circ}C$, and $33^{circ}C$, and then analyzed for specific growth rate and fatty acid composition. Microalgae were cultured in f/2 medium at 23 psu and continuous light of $80{mu}mol$ photons $m^{-2}s^{-1}$. For the I. galbana, growth rates were highest at $29^{circ}C$ and decreased at $33^{circ}C$ to the level observed at $25^{circ}C$. I. galbana (KMMCC12) and Isochrysis sp. cultured at $29^{circ}C$ and $33^{circ}C$, respectively, exhibited the highest growth rates of all Isochrysis species. In terms of fatty acids, I. galbana (KMMCC12) contained higher contents of PUFA and n-3 HUFA at $33^{circ}C$ than did Isochrysis sp. For species of Pavlova, growth rates of P. gyrans and P. viridis at $29^{circ}C$ and $33^{circ}C$, respectively, were higher than those of the other Pavlova species. In particular, P. viridis grew as well at $33^{circ}C$ as it did at $29^{circ}C$. However, P. lutheri and Pavlova sp. did not grow at $33^{circ}C$. In terms of fatty acids, P. viridis cultured at $33^{circ}C$ also exhibited higher contents of PUFA and n-3 HUFA, as compared to P. gyrans. Based on these results, we suggest that I. galbana (KMMCC12) and P. viridis are suitable species for mass culture during the high temperature season.