Cetyltriethylammonium bromide (CTEAB) was considered as a cationic surfactant to form lipoplexes with DNA. In TRIS/HCl buffer, CTEAB self-assembles above its critical micelle concentration (CMC = 0.15 mM) into small spherical micelles as determined by complementary scattering techniques. This surfactant readily interacts with the supercoiled plasmid DNA pBR322 via electrostatics and hydrophobic interactions. Upon increasing surfactant concentration, successive phase transitions are observed from partial neutralization to full compaction of DNA as evidenced by agarose gel electrophoresis, tensiometry, pyrene fluorescence, UV–Vis absorbance and circular dichroism measurements. Under UVA radiation (λ ≥ 335 nm), we show that the presence of the surfactant increases photooxidized damage on DNA especially in the compacted state. A mechanistic study using selective scavengers shows the involvement of singlet oxygen in these oxidative processes due to the direct UVA absorption of DNA itself.