Network structures in the UV-cured resin prepared from bifunctional poly(ethylene glycol) diacrylate (PEDA) were characterized by pyrolysis gas-chromatography (Py-GC) in the presence of organic alkali, tetramethylammonium hydroxide (TMAH). The pyrogram of the uncured prepolymer compound consisting of PEDA and a photoinitiator, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1 (MMMP), were comprised of specific products such as methyl acrylate (MA), intact MMMP, and a series of dimethyl ethers of poly(ethylene glycol) oligomers. Meanwhile, on the pyrogram of the cured resin prepared with the prepolymer compound through UV irradiation, minor but distinctive peaks of methyl acrylate oligomers (MA oligomers) were additionally observed, while those of MA and MMMP considerably lowered as a result of cross-linking formation. The MA oligomers were formed through reactive pyrolysis and methylation selectively occurred at ester linkages of PEDA moieties in the UV-cured resin and were attributed to the sequences of network junctions in cross-linking structure. The observed peak intensities of the MA oligomers thus observed were interpreted in terms of the chain length distribution of network junctions in the cured resin.