Abstarct: Seed deterioration involves loss of quality, viability and irreversible seed vigor loses over time, which is considered to be a major cause of the decline in quality and quantity of production in agriculture. A wide range of secondary mextabolites such as vitamins, growth regulators and antioxidant compounds are used to reduce the deleterious effects of a variety of environmental stresses such as seed deterioration as seed pre-treatment or foliar application.We evaluated the possible antioxidant impact of trans-cinnamic acid, one of the basic secondary mextabolites from the phenylpropanoid pathway as seed pretreatment and foliar application to both unaged and aged cowpea seeds. The study was conducted in both laboratory and field. Laboratory study was performed at Seed Lab of Plant Physiology, University of Wegeningen, The Netherlands as a factorial experiment baxsed on a completely randomized design with four replications. Treatments included seed priming at two levels (unaged and aged seeds) as the first factor and pre-treatment of seed with cinnamic acid at five levels (0, 15, 30, 45 and 60 μM) as the second factor. The field experiment was conducted during 2015 and 2016 as a factorial experiment baxsed on a randomized complete block design with three replications in the laboratory and research farm of Shahroud University of Technology, College of Agriculture, on the cowpea (Bastam local cultivar). The first factor consisted of seed priming at two levels (unaged and aged seeds), the second factor included seed pretreatment with cinnamic acid concentrations at three levels (0, 30 and 60 μM), and the third factor consisted of foliar application of three cinnamic acid concentrations (0, 30 and 60 μM). Seed deterioration resulted in a decrease in germination-related traits, heterophytic growth, and the amount of seed reserves mobilization compared to unaged seeds. The activity of antioxidant enzymes including superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase was also lower in comparison to unaged seeds. Seed aging significantly increased malondialdehyde content. Pretreatment of aged seeds with concentrations of cinnamic acid, 45 and 60 μM, improved all traits related to germination, amount and efficiency reserves mobility and increased activity of superoxide dismutase and catalase. Also, in contrast to the aged seeds, this treatment decreased the activity of antioxidant enzymes and only concentration of 45 μM increased peroxidase activity. Cinnamic acid significantly reduced malondialdehyde in aged seeds. Seed aging in plants from aged seeds decreased plant height, number of branches, number of pods per plant, 1000- seed weight, seed yield, leaf relative water content, plasma membrane stability index, and superoxide dismutase, ascorbate peroxidase and glutathione reductase activity decreased. But they had higher anthocyanin content, flavonoid and catalase activity. Pretreatment of aged seeds with a concentration of 30 μM cinnamic acid resulted in a 12% increase in final yield. Foliar application of cinnamic acid in plants grown from aged seeds with a concentration of 60 μM also increased yield by 21% compared to non-foliar application. But in plants from unaged seeds, foliar application of 30 μM increased the yield by 26.5% compared to non-foliar application. Pretreatment of unaged seeds with different concentrations of cinnamic acid decreased leaf relative water content, membrane integrity index, soluble sugar content, antioxidant enzymes activity except ascorbate peroxidase and increased lipid peroxidation. But concentration of 60 μM improved anthocyanin, flavonoid and free amino acids content. In plants grown from aged seeds, pretreatment and foliar application with concentrations of cinnamic acid (except for the effect of foliar application on anthocyanin content and membrane integrity index) improved physiological traits. Antioxidant enzymes in plants from aged seeds showed different responses to pre-treatment and foliar application of cinnamic acid. pre-treatment and foliar application of this mextabolite resulted in increased superoxide dismutase activity. These treatments decreased the activity of ascorbate peroxidase.