Abstract: Aluminum hydroxide is an effective gastric antacid. In the present investigation, the physical structure and pharmaceutical properties of two samples of aluminum hydroxide tablets have been studied.The tabletting pressure is a fundamental parameter. The effect of pressure on the specific surface area(s), apparent density (d_A), porosity(∈), average pore radius(r), hardness(h), disintegration time (t) and antacid power was determined. It was found that:1. For both aluminum hydroxide tablets and directly compressed tablets, the d_A increased with increasing pressure, while the s, ∈ and r decreased with increasing pressure.2. In the case of directly compressed tablets, the h was proportional to the tabletting pressure up to 5000 psig, but when the pressure was greater than 5000 psig, the h remained constant.3. In the case of aluminum hydroxide tablets, the t increased with increasing pressure, when the pressure was less than 5000 psig, all of the tablets disintegrated within 1～3minutes. When the pressure was greater than 5000 psig, the t was strongly increased.4. For aluminum hydroxide tablets, the tabletting pressure hardly affected the static antacid power, but lower pressure was found to favor faster acid neutralizing velocity of antacids. Also, the dynamic antacid curves show that the time required for acid neutralization to pH 3.0 is proportional to the tebletting pressure, but the acid neutralizing power is almost the same.