In vitro degradation of seven three-dimensional porous scaffolds composed of PLGA85/15, a very useful poly(D,L-lactide-co-glycolide), was performed in phosphate-buffered saline solution at 37 degrees C up to 26 weeks, and effects of porosity (80-95%) and pore size (50-450 mum) on the degradation of the scaffolds were investigated. A series of quantities were measured during the degradation processes: molecular weight and its distribution of PLGA; compressive strength and modulus; and weight, dimension, and porosity of scaffolds. In all of cases with different pore morphologies, the degradation processes obeyed a three-stage model. Scaffolds with a higher porosity or a smaller pore size degraded more slowly than and thus outlasted those with a lower porosity or a larger pore size. The effects are both attributed to a wall effect and a surface area effect because the scaffolds with lower porosities or larger pores possess thicker pore walls and smaller surface area, which depress the diffusion of acidic degradation products and thus results in a stronger acid-catalyzed hydrolysis. This work suggests that, in designing a tissue-engineering scaffold composed of PLGA and adjusting its degradation rate, the effects of pore morphologies should be taken into consideration in addition to those of chemical composition and condensed state of raw materials.