Microplastics in aquatic environments are very important global pollutants. However, few empirical studies have reported the direct settling behavior of microplastics in aquatic environments. This study presents the behavior and behavioral evaluation method of microplastics, utilizing eco-friendly standardized microplastics of discarded plastics. Microplastics of polyvinyl chloride standardized in this study settle under both stagnant state and vigorous shaking movement in waters, while all microplastics of polyethylene, polypropylene, and polystyrene float. Although most microplastics of polyethylene terephthalate float on water in a stagnant state, most of them are settled by shaking movement of waters. By assessing (or pre-assessing) the behavioral density of microplastics, this study provides a baseline and clues to understanding the distribution and transport of microplastics in aquatic environments.