Abstract Flower-like Bi2O2CO3 was synthesized in an aqueous solution containing bismuth nitrate, citric acid and urea. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption–desorption and UV-visible diffuse reflectance spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange in an aqueous solution under Xe lamp irradiation. The effects of citrate ion on the morphology and photocatalytic activity were investigated. The results show that citrate ions facilitate the formation of hierarchical flower-like Bi2O2CO3 microsphere. The amount of citric acid is an important parameter to control the morphology and size of Bi2O2CO3 microsphere. The flower-like Bi2O2CO3 exhibited an enhanced photocatalytic activity than Bi2O2CO3 blocks. The highest photocatalytic performance can be achieved for the Bi2O2CO3 microspheres synthesized in the solution with the C6H8O7/Bi(NO3)3 M ratio of 2:1 due to the synergic effects of several factors, including its better crystallinity, larger surface area, stronger UV-visible absorption and unique hierarchical microsphere structure.