The present invention produces entrapping immobilization pellets which have high pellet strength and retain high and stable microbial activity (nitrification activity) even if a low concentration of a material involved in immobilization (such as an immobilizing material or polymerization initiator) used. The entrapping immobilization pellets in which microorganisms are entrapped and immobilized in an immobilizing material comprise a filler having a plate-like and/or needle-like crystal structure in the immobilizing material.