Phenolic wastewater is one of the common industrial pollution sources. Ozonation with brucite and natural hydroxide magnesium has more effective impact than single ozonation of phenol degradation. The function of brucite in ozonation of phenolic wastewater was discussed previously as OH^- from hydrolyzed Mg(OH)₂ forming basic catalyst and raising the activities of O₃. In this study, two batch experiments with different brucite-phenol ratios were carried out with close attention paid to the final sedimentary products. The experiments show that Mg²⁺ from hydrolyzed Mg(OH)₂ could combine with intermediate products of phenol oxidation to form indissoluble deposits and raise the processes of phenol degradation. When the initial concentration of phenol was 47 g/L, and the controlled dosage of brucite by C/Mg (atoms ratio of carbon to magnesium) equal to 30, the only residual solid after 3 hours O₃ aeration was glushinskite (magnesium oxalate dihydrate) which substituted for the brucite, as supported by XRD and TG/DSC examination. At the terminal of the reaction, the test solution showed pH below 4 and removal of nearly 40% of TOC (Total Organic Carbon). In a comparative experiment changing the initial concentration of phenol to 1.5 g/L with C/Mg (atoms ratio) equal to 1 and under the same condition of O₃ aeration, the residual solid of the exam was still brucite, the terminal pH was 10 and 92.8% of TOC was removed. The results from two examinations reveal that the process of ozonation of phenolic wastwater is characterized by continued acidification. At least under the higher initial C/Mg ratio condition, the primary proton can neutralize hydroxyl from hydrolyzed brucite. In this case the terminal sediments are only glushinskite. Obviously, Mg²⁺ is derived from hydrolyzed of brucite; however, glushinskite is stable in an acidic environment. Both Mg²⁺ and OH^- from brucite play a role of degrading phenol in water.