Flower-like basic magnesium carbonate(BMC) was fabricated by hydrothermal method. Magnesium solutions are precipitated by sodium carbonate in the presence of cetyltrimethylammoniumbromide(CYAB). Particles were synthesized by various concentration of substance, reaction time and temperature. The samples were characterized by FE-SEM, EDS, XRD, FT-IR and PSA. It found that BMC were synthesized and some sample was composed of flower-like micro particle which are interweaved by a lot of nano-sized thin sheet. After the calcination for BMC at 600 ℃ for 12 h, BMC were completely converted to MgO. The catalytic properties of prepared MgO for the ozonation of phenol were evaluated. Prepared MgO revealed good separability and remarkable catalyst for the degradation of phenol.