The encapsulation and catalytic efficiency of organophosphate hydrolyzing enzymes in polymer-stabilized nanocapsules is reported. Polymerized vesicles - derived from a headgroup-polymerizable phospholipid, 1,2-dipalmitoyl-sn-glycero- 3-phosphoN-(2-hydroxymethyl)-3,5-divinylbenzamide (DPPE-DVBA)-containing enzymes were used as catalytic nanocapsules. Three enzymes, organophosphorus hydrolase (OPH), phosphotriesterase (PTE), and organophosphorus acid anhydrolase (OPAA), were encapsulated in vesicles by incubating them with freeze-dried vesicles at 55C, followed by intermittent vortexmixing. Enzyme-containing vesicles, collected after gel-filtration, were stabilized by photopolymerization at 254 nm to yield crosslinked catalytic nanocapsules. The nanocapsules containing OPH and PTE showed specific activities of 0.36 and 1.74 molmg -1min-1, respectively, against methyl parathion (MPT), and OPAA-containing nanocapsules showed a specific activity of 57.1 molmg -1min-1 against diisopropylfluorophosphate. Freeze-dried, OPH- and PTE-containing nanocapsules showed retentions of 83 % and 85 % specific activity, respectively, upon redispersion in buffer solution. Three-week, room-temperature storage of OPH-containing nanocapsules showed a retention of 18% enzyme activity. Hydrolysis of MPT in crosslinked DPPE-DVBA/OPH vesicles showed that hydrophobic MPT permeated through the bilayer membrane of the freeze-dried nanocapsules, releasing the hydrolysis product para-nitrophenol, which permeated back to the exogenous dispersion medium leaving the enzymes free to react with freshly permeated MPT in the interior of the nanocapsules. 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.