With tremendous increase in development of nanotechnology, there is a developing enthusiasm toward the application of nanoparticles in diverse areas. Carbon nanotubes, fullerenes, quantum dots, dendrimers,iron oxide, silica, and gold and silver nanoparticles are frequently used in different applications such as drug delivery, ceramic materials, semiconductors, electronics, medicine, cosmetics, etc. Some of these nanoparticles have shown major toxic effects on fauna, flora, and human beings, such as inflammation, cytotoxicity, tissue ulceration, and reduction of tell viability. Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MW-CNTs) can induce oxidative stress and fibrosis in the lungs Of rat and mice., SWCNTs can also induce oxidative stress to the nervous system in human beings. Inflammatory injury and respiratory distress can be observed, due to TiO2 nanoparticles with small diameter. Nanoparticles can also pose detrimental effects on plants, such as decreased growth rate, genomic and proteomic changes, etc. Toxicity of nanoparticles arises because of their specific characteristics, such as greater "surface area to volume ratio" compared with bulk particles of the same chemistry. The objective of this review is to critically evaluate the current literature on the toxicity of nanoparticles.