The rapid development and consequent release of toxic compounds have raised significant concerns due to their potential of causing environmental hazards. The natural and human-engineered ecosystem is now being increasingly subjected to risk from release of these toxicants in the environment. Several laboratory-based studies indicate the use of plants in ecological risk assessment due to their remarkable ability to bio-accumulate toxins. Plant species show different levels of phytotoxic response, depending on types, concentrations, and chemical states of toxicants. Plants respond to different types of toxicants by altering their photosynthetic pigment content, root length, shoot length, biomass production, seed germination, and enzyme activity. It is clearly evident that plants possess a variety of physiological and biochemical mechanisms for tolerating stress induced by toxicants. However, phytotoxicity data for plant species have not received much attention in decision-making processes concerning the environmental risk of toxicants. In addition, long-term effects of different doses of toxicants and the behavior of the mixture of toxicants in ecosystems are yet to be more thoroughly studied. Given the large increase of toxicant production and release, mainly from anthropogenic sources, there is an urgent need to perform ecosystem-level studies to obtain complex information on the impact of toxicants in the environment and to test the suitability of plant species in natural field conditions. This chapter describes the potential of phytotoxicity in ecological risk assessment.