Differential thermal investigation was made of amorphous hydrous ferric oxides, precipitated on neutralization of ferric chloride solution under different laboratory conditions, ranging from DOC to 85°C in temperature, and from 3 to 12 in pH. Each of the differential thermal curves obtained shows an endothermic peak due to the release of adsorbed water, followed by a exothermic peak due to crystallization of anhydrous ferric oxide to hematite. The temperature corresponding to the exothermic peak varies in the range from 240°C to 460°C accrding to the temperatures and pH values of the solution from which the hydrous ferric oxide is precipitated.