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The invasive plant, Sphagneticola trilobata (L.) J. F. Pruski, has been known for its bioactivities and used to synthesize gold nanoparticles (AuNPs). Nonetheless, previous research has not directly compared the effectiveness of the plant parts in producing the AuNPs. The objective of this study was to compare the effectiveness of the flower and leaf of S. trilobata in synthesizing AuNPs. S. trilobata leaves and flowers were separately extracted using distilled water at 60°C for 30 min. The leaf and flower extracts were mixed with the HAuCl. 3H2O and heated to 60°C for 30 min to yield AuNPs-ALSt and AuNPs-AFSt, respectively. AuNPs were also prepared using trisodium citrate (Na3C6H5O7) as a control. The resultant AuNPs were characterized using an ultraviolet-visible spectrophotometer, particle size analyzer, and scanning electron microscope. Antioxidant activity was evaluated based on 1-diphenyl-2-picrylhydrazyl (DPPH) inhibition and anticancer activity– 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide assay against MCF-7 cells. The AuNPs-ALSt and AuNPs-AFSt were revealed to have better stability and smaller particle diameters. AuNPs-ALSt and AuNPs-AFSt had average particle diameters of 11.86 ± 3.37 and 34.86 ± 23.56 nm, respectively. Agglomeration was predominantly observed in AuNPs synthesized using the flower or leaf extract as stipulated to be affected by the insufficient capping agent and intense hydrolytic reaction. AuNPs-AFSt had higher DPPH antioxidant activity than AuNPs-ALSt with half-maximal inhibitory concentrations of IC50 123.44 and 168.83 ppm, respectively. Both AuNPs-ALSt and AuNPs-AFSt could inhibit 80% growth of the MCF-7; however, at lower concentrations, inhibitory effects were more pronounced in AuNPs-AFSt. Aqueous extracts of S. trilobata flowers and leaves could be used to synthesize AuNPs, whereas the former yielded AuNPs with higher biological activities.