Abstract: Four kinds of co-composite matters including alginate, agar, calcium carbonate and activated carbon were mixed with polyvinyl alcohol (PVA) for immobilizing the manganese-oxidizing bacteria. The internal structure of the PVA gel beads was tested and analyzed by scanning electron microscope. A dense layer exists in the surface of PVA gel beads with an unequal distribution, and adding agar is useful for overcoming this shortcoming and increasing the number of internal pore. Adding calcium carbonate decreases the diameter of the gel beads and improves the thickness of the internal pore wall. The solution and expansion of PVA beads may be worsen after adding sodium alginate and agar and better with activated carbon and calcium carbonate. All the four kinds of co-composite matters are useful for improving the mechanical strength of the PVA gel beads until the ratio is lower than 1%. Activated carbon and calcium carbonate relate with the improving of the bioactivity and mechanical strength, respectively.