A simple and eco-friendly method has been developed for the synthesis of gold nanoparticles using allamanda flower extract. In this green synthesis method, chloroauric acid (HAuCl4) solution was reduced with the help of allamanda flower extract. The synthesized gold nanoparticIes were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and x-ray diffraction technique for their morphological and structural analysis. The size of the spherical and triangular gold nanoparticIes was found to be in the range of 5-40 and 20-70 nm, respectively. The x-ray diffraction analysis revealed that the crystallite size of face-centered cubic (FCC) gold nanoparticles was ~ 11 nm. These synthesized gold nanoparticles exhibit good catalytic activity towards the reduction of H2O2. The fabricated sensor exhibits good sensitivity of 21.33uA/ mM/cm2 with linear relationship (R2 = 0.996) in the range from 2 to 10 mM of H2O2 concentration. This work can be extended further for potential applications such as antimicrobial studies, bio-imaging and drug-delivery owing to the known properties of the allamanda flower extract.