This paper focuses on magnesium oxide and hydroxide, which are compounds with favorable and exclusive features for various applications. Magnesium oxide nanoparticles (MgO NPs) have been reportedly produced through green synthesis procedures. Natural materials or their products including plants extracts or those of plants parts, roots, fruits, and gums have been used as reducing and capping agents in the synthesis procedures. MgO nanostructures have been reportedly used in drug delivery, anti-cancer and anti-bacterial applications, which has increased the risks of human exposure to these materials. A full understanding of the influence of MgO NPs and the underlying mechanisms of their actions are important in evaluating the environmental risks of using these nanoparticles. MgO NPs are known to enjoy high biocompatibility and stability, and low IC50 values in comparison with copper, manganese, tin, cobalt, manganese oxide nanoparticles. This has been attributed to the great bioavailability, and lower toxicity (hemolytic investigations) of these particles. MgO NPs are also known as effective chemotherapeutic and bacteriostatic agents for use in the fast detection and diagnosis of various cancers. However, more studies should be aimed at evaluating the toxic effects of MgO NPs on individual organism. As a first step, this review attempts to shed some light on the advancements in the area of green synthesis for preparing efficient NPs including MgO for future applications.