Photodegradation of a herbaceous lignin and unsaturated polyester was carried out with a novel TiO2/polyethylene oxide (PEO) + methyl linoleate (ML) photocatalyst system. The lignin and unsaturated polyester photodegradation ratios were 51 and 40 %, respectively, showing that the TiO2/PEO + ML had high photocatalyst activity. The ML· produced by the TiO2 photocatalyst was able to attack the lignin and unsaturated polyester because of its hydrophobic molecular structure and worked well as the initiator. In order to study the detailed mechanism of photodegradation with the TiO2/PEO + ML, the chloroform soluble fraction of the photodegraded unsaturated polyester was characterized with 1H-NMR measurement. The result showed that the TiO2/PEO + ML preferentially cleaved carbon–carbon bond.