Photoreaction of a series of p-phenylenediacrylic acid (p-PDA) monoester was investigated in the organized system such as crystals monolayer and multilayer (LB) films. p-PDA monoesters having a shorter alkyl chain than dodecyl residue, are photoreactive crystals. They gave oligomers on irradiation. p-PDA monoesters with a longer alkyl chain than decyl residue, could form stable monolayers and photoreactive LB films were prepared successfully. Photochemical reaction of LB films proceeded by cyclo-addition of double bonds forming oligomers and polymers. The mixed LB film with octadecylamine showed different photoreactivity from that of p-PDA monoester LB film.