The comb-type polyelectrolyte, poly(ethylene glycol)-graft-poly(allyl amine) (PEG-g-PAA), was synthesized to prepare polyion complex (PIC) micelles with Aspergillus Niger Glucose oxidase (GOD). Even after mixing GOD and PEG-g-PAAs with various PEG contents, the resulting mixtures remained transparent but the mixture of GOD and PAA homopolymer immediately precipitated. In the mixtures prepared with a stoichiometric mixing ratio, the formation of PIC micelles with a core-shell structure was suggested from dynamic and static light scattering measurements. Glucose, the substrate for GOD, could easily diffuse into the PIC micelles, and the GOD molecules were active even in the core of the PIC micelles. GOD didn't lose its enzymatic activity through entrapment into the PIC micelles. (C) 2008 Wiley Periodicals, Inc.