Using medicinal extracts is one of the most important alternative methods for producing nanoparticles, due to it is safe, biocompatible and eco-friendly. Hyoscyamus muticus leaf extract was used in this study for the green synthesis of Magnesium Oxide nanoparticles (MgO NPs) by mixing it with a solution of magnesium nitrate. Several techniques were done to characterize the obtained material, including Scanning Electron Microscopy (SEM), Ultraviolet-Visible (UV-Vis) Spectroscopy, X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). Aspergillus ochraceous (A. ochraceous) and Aspergillus niger ( A. niger) were incubated at different temperatures. The results indicated that 27°C and 35°C were the optimum temperatures for the growth, respectively.  The effect of MgO NPs on the growth and metabolism (α-amylase) of A. niger and A. ochraceous were studied under optimum temperatures. It was observed by adding MgO NPs at concentrations of 0.25%, 0.5% and 1%; fungal growth was inhibited with 11%, 19% and 89% for A. niger and 67%, 76% and 100% for A. ochraceous. The metabolism of Aspergillus species as α-amylase was completely prevented at all concentrations of MgO NPs. The purpose of this research is to compare the effects of climate change factors and MgO NPs on the growth of A. niger and A. ochraceous and α-amylase production.