Mesoporous silica nanoparticles (MSNs) are composed of silicon and oxygen, have 3 nanometer pores, and >100 nm diameters. MSNs of two different pore structures – MCM-41: straight, parallel pores; and WO: interconnected, disordered pores – were synthesized for drug delivery (drug transportation to reduce side effects) of doxorubicin (DOX), an anti-cancer drug that causes heart damage. The release of DOX was measured to determine the effect of pore structure. These studies are crucial to optimize MSN architecture for drug delivery.