Abstract: Phaeocystis globosa frequently causes extensive harmful algal blooms in coastal waters of China. It has unusual life cycles, transferring between solitary cell and colonies. Solitary cells are generally a few microns in diameter, but colonies are up to 3 cm in diameter. The giant colony may result in its unique structure and cell distribution. We measured the colony diameter, colony-cell abundance and solitary-cell abundance in P. globosa (Shantou strain, isolated from South China Sea in 1997) to investigate the relationship of colony architecture and cell distribution. The results showed that colony is the dominant form during the polymorphic life cycle of P. globosa, with contributions of 38% to 95% to total biomass, especially in the late exponential and stationary phases, when colony-cell abundance assumed absolute superiority over solitary cells. Log colony-cell abundance increased with log colony diameter with the slope of 1.34 on the regression line; whereas the value was significantly lower than those in the previous studies. Therefore, the colony of P. globosa (Shantou strain) contains relatively fewer cells per unit surface area, which means the Shantou strain differed from other strains in colony architecture and cell distribution. P. globosa from Shantou can form a giant colony, which effectively protects against predators and may significantly influence the food web structure and function in regions with P. globosa blooms.