Atrazine is a widely used herbicide on many crops and is considered one of water pollutant with approved biological hazards on plants, animals and human. Vicia faba seedlings as a biological system, is used to investigate the genotoxicity of Atrazine. Also, Nano selenium (N-Se), a Nano particle with reactive oxygen species scavenging activity was applied to reduce the genotoxicity of Atrazine. Atrazine treatment at concentration of 35 mg/L is applied. Two concentrations of N-Se (10 and 20 ppm) were used alone and in combination with Atrazine (35 mg/L) in addition to control treatment. Changes in germination percentage, shoot and root length, hydrogen peroxide (H 2 O 2) content, lipid peroxidation product malondialdehyde (MDA), chromosomal aberrations, and mitotic index were determined. Semi quantitative RT-PCR analysis (sqRT-PCR) was applied to investigate associated changes in expression pattern of some stress related genes such as antioxidant enzymes, heat shock proteins (HSP17.9, HSP70.1), photosystem II (PSII) and Metalothioniene (MT). Atrazine treatment recorded the lowest germination percentage and caused a reduction in shoot and root length. Significant increase in H 2 O 2 value, MDA contents, and chromosomal abnormalities percent resulted in Atrazine treatment. Noticeable suppression in expression level of all studied genes was accompanied with Atrazine treatment. N-Se, in its two concentrations with Atrazine causing a reduction in all severe effects of Atrazine and improving seedlings performance. Treatments with N-Se induced the expression of MT gene with increase in expression level alongside increase in the concentration of N-Se. This is one of rare studies that investigate the biological effects of N-Se in vivo anti-mutagenesis of Atrazine as well as a first record of Nano metalic particles N-Se as inducer for MT genes.