In order to modify the structure of phosphorylated polyvinyl alcohol (PVA) gel beads for improving their gas permeability, some additives such as soluble starch, partially saponified PVA, and calcium alginate were used. An addition of a small amount of calcium alginate to gel solution during gelation was made. The calcium alginate was later destroyed by treating the beads with phosphate solution, thereby effectively promoting the ability of gas permeation. The modification process with alginate would not cause a significant decrease in the nitrate reduction rate of immobilized beads. The gas permeability of beads increased as high as 62%.