Nanoplastics are likely ubiquitous in the environment, and their potential toxic effects are a concern. However, quantitative information about the distribution of nanoplastics is still lacking, and toxicity tests are limited to a few select polymers because of the lack of appropriate standard materials, which should be nanoscale particles with standardizable morphologies, properties comparable to those of commercial polymers, and no impurities. Here, a precipitation‐based method for preparing spherical nanoscale particles without the introduction of impurities is developed. The similarity of the molecular weight distributions, crystallinities, and thermal properties of five major polymers prepared using this method—low‐density polyethylene, high‐density polyethylene, polypropylene, polyvinyl chloride, and polystyrene—to those of commercial polymers indicate their potential for use as standard nanoplastic particles. This study provides a fundamental approach for the synthesis of standard nanoplastic particles that will facilitate quantification of the concentrations of nanoplastics in the environment and tests of their toxicity, which are required to assess the risks associated with exposure to them. This paper reports precipitation‐based methods for preparing spherical nanoscale particles of five major polymers—low‐density polyethylene, high‐density polyethylene, polypropylene, polyvinyl chloride, and polystyrene—without the introduction of impurities. Subsequent analysis reveals their potential for use as standard nanoplastic particles that could facilitate quantification of the concentrations of nanoplastics in the environment and determination of their toxicity.