The fractal theory has been applied to study surface complexity where surface aspects influence physical properties and play a role in controlling heterogeneous reactions at interfaces. In this work, the influence of the fractal character of some selected antacids was investigated in regard to their neutralizing activity. The materials used were magnesium trisilicate, magnesium hydroxide, and heavy and light magnesium oxide, each from three different manufacturers. Surface area, total pore volume, and particle size were measured. Fractal dimension was determined from gas adsorption data according to pore size distribution, the Frenkel-Halsey-Hill, and thermodynamic methods. The results obtained show a correlation between neutralization activity and fractal character father than total surface area or particle size. Also, the effect of porosity in terms of total pore volume was modified by the structure of the porous network. The complexity of the pore network played a major role in controlling reactivity. However, the effect of surface roughness was only demonstrated when adsorption on the surface was a rate-limiting step in the reaction.