To prevent or treat diseases in which active oxygen is involved such as inflammatory cell injury, diabetic diseases (nephropathy, retinopathy, and neuropathy), ischemia and reperfusion injury, renal failure, rheumatoid arthritis, and myocardial infarction, a process for producing an aqueous colloid of graphite silica particles emitting far-infrared rays, the process comprising adding graphite silica (black silica) particles emitting far-infrared rays to water, is provided.