ZnO nanoparticles (ZnO-NPs) were successfully fabricated by soft chemical technique from zinc acetate di-hydrate (Zn(CH 3COO) 2·2H 2O) and octadecylamine (CH 3 (CH 2) 17NH 2). The crystallinity of the grown product was analyzed by the XRD technique revealing the as-prepared nanoparticles (NPs) have hexagonal wurzite structure. Their morphology was investigated by FE-SEM and TEM, which showed that well dispersed spherical particles of 10 ± 4 nm in diameter had been formed. The optical property of ZnO-NPs was confirmed by the photoluminescence spectroscopy showing an intense room temperature photoluminescence in the violet region of 382 nm. Furthermore, the synthesized ZnO-NPs showed a better photo-catalytic activity than that of commercial Degussa P-25 powder during photochemical degradation of methyl orange (MO) dye. Also, the Zn 2p1/2, Zn 2p3/2, and O 1S peaks in XPS clearly suggest that the grown nanoparticles are ZnO. Additionally, liquid chromatography mass spectroscopy (LC–MS) was applied to observe the degradated compounds from photo-catalytic degradation of methyl orange (MO) dye in presence of ZnO-NPs.