Iron oxide nanoparticles have recently been proposed as an efficient and environmentally friendly material for wastewater treatment. In comparison to chemical and physical approaches, green nanoparticles synthesis method that employs microalgae or plant extract is regarded as more cost-effective and environmentally friendly. In this study, iron oxide nanoparticles were synthesised using Chlorella vulgaris extract, and their feasibility in removing crystal violet dye from wastewater via photocatalytic degradation was investigated. Iron oxide nanoparticles was synthesized by adding C. vulgaris extract to 0.1 M iron (III) chloride solution. The X-ray diffraction (XRD) peaks revealed that the iron oxide nanoparticles were crystalline in nature. The nanoparticles were also analysed using Field Emission Scanning Electron Microscope (FESEM), revealing a sphere with cylindrical shape of about 109 nm in size, with the Energy Dispersive X-ray (EDX) elemental analysis showing the highest proportion of O followed by Fe. The ability of iron oxide nanoparticles to remove crystal violet dye in the dark and in the presence of ultraviolet (UV) light was investigated. The percentage removal was consistently higher under the presence of UV lamp at all durations tested (30 - 90 minutes), indicating the feasibility of iron oxide nanoparticles to photodegrade crystal violet dye. © Published under licence by IOP Publishing Ltd.