In this paper use of marine macro alga Sargassum wightii in Green orchestration of Gold nanoparticles is reported. In this work, the optimum parameters were encountered to be 30ºC at pH 10 and 100 ppm aurochlorate salt. The contribution of nitrate reductase was studied using biochemical assays. The nitrate reductase activity was found to be reduced from 0.6245 mmole/min/gram to 0.4244 mmole/min/gram after fabrication of gold nanoparticles. The morphology was studied using electron microscopy which showed presence of isotropic spheres along with anisotropic nanoparticles and the size was found to between 30-100nm . The crystalline nature of gold nanoparticles was examined using XRD and was found to be face centered cubic.