Abstract: The increasing number of organic contaminants in the environment seriously harms the ecological environment and human health. Previous studies have often neglected the effect of molecular clusters of organic contaminants (MCOCs), which may alter the physicochemical properties of organic contaminants and thus affect their environmental behavior and fate. The molecular structure properties and environmental conditions determine the states of organic contaminants (molecular, ionic, cluster and precipitation states), which further determine their environmental behavior and risk. For example, clusters may be more beneficial to their rapid adsorption than other occurrences, but large size may also limit their activity within the pores. This paper reviews the factors that determine the occurrence of organic contaminants (polycyclic aromatic hydrocarbons, phthalates, and other organic pollutants) and their environmental behaviors and fates. Accordingly, the universality and significance of MCOCs formation were summarized, and their environmental behaviors, fates, and potential environmental risks were emphasized. This paper aims to provide theoretical support for the research on organic contaminants' environmental behavior and fates and their pollution control.