Conjugated polymers have a high conductivity that comes from pi electron delocalization. However, they can be easily oxidized and lose their properties by oxygen in air. Therefore, the photostability enhancement of conjugated polymers is a significant issue in their applications. we prepared conjugated polymer nanoparticles assembled with phospholipids via forming phase separated films followed by shattering the films. The phospholipids are highly bound to the polymer through an alkyl chain between the polymer side chain and the lipid alkyltail. We investigated the effect of the alkyl tail length of the phospholipids on the photostability of nanoparticles of conjugated polymers.