Sol-gel derived silica particles are candidates for vehicles for injectable controlled drug-delivery. In this study, Proteinase K was the model biomolecule encapsulated in the silica xerogel, ambigel, and aerogel particles. The surface area and average pore diameter of these particles are reported. Both the amount of Proteinase K released from the particles and the activity of the released Proteinase K were measured as a function of time. The primary finding of this study is the effect of pore diameter on the specific activity of Proteinase K released from these particles.