Allelopathy is a common phenomenon in nature and can be defined as any direct or indirect effects of one plant on the other one (including microbes) through the release of plant produced secondary products (allelochemicals) into the environment by ways of leaching, volatilization, root exudation, and decomposition of residues. When the effect of the allelochemicals is to inhibit the growth and development of receptors, it is considered as a biotic stress called allelochemical stress. The allelochemical can result in the obvious cytotoxicity to receptor plants, affect the generation and survival of root border cells, a population of viable cells that are attached to the root apex in a one-cell layer in a manner similar to that of white blood cells functioning in the defense. Allelochemical-treated cells exhibit irregular arrangement and shape, and altered the structure of cell walls, plasma membrane, and certain organelles including mitochondria, chloroplasts, Golgi apparatus, vacuoles, etc. The allelochemical also has genotoxicity to receptor plants by interfering with DNA replication, cell division, and gene expression pattern. Chromosomal abnormalities, such as the break, lag, and conglutination of chromosomes, formation of micronucleus and nuclear buds and chromosomal bridges and rings, and three pole divisions was often observed. As a resultant, the mitotic index was significantly reduced in cells exposed to allelochemicals. The allelochemical causes the changes of DNA molecular marker genotype (DNA chain type) in terms of variation in band intensity, or the loss of bands and appearance of new bands. The gene expression pattern in allelochemical-treated plants is changed and different genes are up-regulated, down-regulated, transient-expressed, or continuous-expressed, respectively. Furthermore, allelochemical treatment enhances the production of reactive oxygen species (ROS), the toxic metabolic products in plants and other aerobic organisms. However, the activities of ROS scavenging enzymes such as catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) are decreased. Such imbalance results in the oxidative stress, which is regarded as a common phenomenon caused by allelochemical stress. The enhanced production of ROS leads to the peroxidation of lipid and damages to macromolecules such as proteins, nucleic acids and lipids. As a resultant, the membrane permeability and the content of malondialdehyde (MDA) are increased. The increased level of ROS can also be the signal to activate the relevant signaling cascade and ultimately to trigger genome-wide changes in gene expression. As a resultant, the apoptosis is induced and the cellular injury and plant growth inhibition are observed in receptor plants. Oxidative stress induced by allelochemical treatment might be a cause of apoptosis in receptor plants. In conclusion, allelochemical stress interferes with the defensive function of root border cells, induces cell damage, genetic damage, and oxidative damage of receptor plant cells. Elucidation of the relevance between the cell damage and oxidative damage induced and the mechanism of the response of root border cells to allelochemical stress would be expected to be a trend in the future to reveal allelopathic mechanisms.