The objective of this study was to investigate the delivery and activity of a vascular endothelial growth factor (VEGF) antisense oligonucleotide in a human retinal pigment epithelial cell line (ARPE-19) using a biodegradable nanoparticulate delivery system. A 19-mer antisense phosphorothioate oligonucleotide (PS-ODN) complementary to bases 6-24 relative to the translational start site of the VEGF mRNA, a sense PS-ODN and a mismatch PS-ODN were examined for the inhibition of secretion and mRNA expression of VEGF using an enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Nanoparticles of the antisense oligonucleotides were formulated using a poly(lactide-co-glycolide) (50:50) copolymer using a double emulsion solvent evaporation method. After preparing nanoparticles, drug loading, encapsulation efficiency and particle size were determined. The cells were exposed to either plain solution of oligonucleotide or nanoparticles of oligonucleotide from Day 3 through Day 6. Alternatively, the cells were incubated with PS-ODNs and lipofectin for 4 h on Day 4. In all studies, VEGF secretion and mRNA expression were determined on Day 6. The particle size, drug loading and encapsulation efficiency were 252 nm, 5.5% and 16.5%, respectively. The antisense PS-ODN inhibited VEGF mRNA and protein secretion when delivered using nanoparticles or lipofectin but not in its free form. This was consistent with the ability of nanoparticles and lipofectin to elevate the cellular uptake of the oligonucleotide by 4-fold and 13-fold, respectively. Neither mismatch nor sense oligonucleotides inhibited VEGF secretion. In conclusion, biodegradable nanoparticles enhance cellular delivery of a VEGF antisense oligonucleotide and inhibit VEGF secretion and mRNA expression in a human retinal pigment epithelial cell line.