This study investigated the synthesis and photocatalytic activity of zinc oxide (ZnO) nanoparticles (NPs) at room temperature (ZnO-RT), 60° C (ZnO-60), and ultra sonication (ZnO-US). The NPs were made from Cucumis maderaspatanus (Cm) extract. ZnO NP sizes and shapes were observed to be influenced by synthesis conditions, as demonstrated by characterization techniques includes scanning electron microscopic analysis (SEM) and Fourier Transform Infra Red analysis (FTIR). The heated (60 °C) and ultra sonication (US) conditions produced NPs with diameters in the range of 15–25 nm with spherical shapes, while the non-heated (RT) condition produced NPs with diameters in the range of 20–30 nm with a mixture of spherical and flower shapes confirmed by SEM. Additionally, the presence of the reducing agents in the herbal extract was verified by analysing the FTIR spectra of the extract obtained after the synthesis. By using Coomassie Brilliant Blue R-250 (CBB-R-250) (50 ppm) as a probe molecule and subjecting it to UVA irradiation (λ = 356 nm), photocatalytic activity was measured. The results showed that ZnO-US reached 100 % degradation after 120 min and 90 % of the pollutant was mineralized, while ZnO-60 and ZnO-RT showed results of 80 % and 48 %, respectively. According to this study, the biological synthesis of NPs using plant extracts can be considered as a cost-effective and efficient method of biological synthesis of NPs and it could be an appropriate replacement to typical chemical methods for the synthesis of NPs.