Biodegradable and non-biodegradable microcapsules were prepared via the layer-by-layer (LbL) technique consisting of the polyelectrolyte pairs of dextran sulphate/poly-L-arginine and poly(styrene sulfonate)/poly(allylamine hydrochloride), respectively, in an attempt to encapsulate plasmid DNA (pDNA) for efficient transfection into NIH 3T3 cells. Results indicated the retention of bioactivity in the encased pDNA, as well as a correlation between the level of in vitro gene expression and biodegradability properties of polyelectrolyte. Furthermore, the incorporation of iron oxide nanoparticles within the polyelectrolyte layers significantly improved the in vitro transfection efficiency of the microcapsules. As a novel pDNA delivery system, the reported biodegradable microcapsules provide useful insight into plasmid-based vaccination and where there is a prerequisite to deliver genes into cells capable of phagocytosis. (c) 2012 American Institute of Chemical Engineers Biotechnol. Prog., 28: 10881094, 2012