Graft copolymer polyethylenimine--graft--poly(N-vinylpyrrolidone) (PEI-g-PVP) was prepared by coupling mono carboxyl-terminated PVP (PVP--COOH) with PEI using N,N''-dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (NHS) as coupling agents. In aqueous medium, PVP--g--PEI can self-assemble into stable polyion complex micelles with an oppositely charged block copolymer, poly(N-vinylpyrrolidone)--block--poly(2-acrylamido-2-methyl-1-propanesulphonic acid) (PVP-b-PAMPS). Transmission electron microscopy images showed that these micelles were regularly spherical in shape. The micelle size determined by size analysis was around 142 nm. To estimate their feasibility as vehicles for drugs, the model drug folic acid (FA) was incorporated into the cores of the micelles via electrostatic interactions. In vitro release test of FA showed that the drug-release rates are dependent on the pH value of the release media. Based on these results, we can conclude that the polyion complex micelles prepared from the PEI-g-PVP/PVP-b-PAMPS copolymers have great potential as drug delivery nanocarriers.