Objectives Rapid increase in engineered nanoparticles (ENPs) in many goods has raised significant concern about their environmental safety. Proper methodologies are therefore needed to conduct toxicity and exposure assessment of nanoparticles in the environment. This study reviews several analytical techniques for nanoparticles and summarizes their principles, advantages and disadvantages, reviews the state of the art, and offers the perspectives of nanometrology in relation to ENP studies. Methods Nanometrology is divided into five techniques with regard to the instrumental principle: microscopy, light scattering, spectroscopy, separation, and single particle inductively coupled plasma-mass spectrometry. Results Each analytical method has its own drawbacks, such as detection limit, ability to quantify or qualify ENPs, and matrix effects. More than two different analytical methods should be used to better characterize ENPs. Conclusions In characterizing ENPs, the researchers should understand the nanometrology and its demerits, as well as its merits, to properly interpret their experimental results. Challenges lie in the nanometrology and pretreatment of ENPs from various matrices; in the extraction without dissolution or aggregation, and concentration of ENPs to satisfy the instrumental detection limit.