Outdoor cultivation of Isochrysis galbana is often limited in summer, a season with strong sunlight. In this study, we aimed to construct consortia of I. galbana and bacteria with increased resistance to light stress. Twenty-eight bacterial strains were isolated from a cultivation pond of I. galbana. Seven bacteria strains were found to grow in supernatant of I. galbana culture. Among these strains, four strains (E4, E12, E51, and E47) were found to promote algal growth when co-cultured with axenic I. galbana. Compared with axenic I. galbana culture, co-cultures with the bacterial strains E4 or E51 exhibited significantly smaller decreases in maximal photochemical efficiency of photosystem II (PSII) (F_v/F_m) under high light, demonstrating bacteria-mediated mitigation of photoinhibition in I. galbana cells. Further analysis showed that the microalgal-bacterial consortia (I. galbana/E4, I. galbana/E51) suffered from lower excitation pressure on PSII and had higher efficiency of excitation energy capture by open PSII reaction centers and photosynthetic electron transport rate, when compared with axenic I. galbana culture. Furthermore, the bacteria E4 and E51 affected accumulation of proteins and polysaccharides in the bound and supernatant fractions in the I. galbana cultures. This study presents the first demonstration that certain bacteria contributed to mitigate photoinhibition in I. galbana cells.