Plant polyphenols exhibit a wide variety of biological activities such as antimutagenicity, anticarcinogenicity and antioxidative activity. There is no report whether gallic acid (GLA), a naturally occurring plant phenol, is able to activate the plant defense system under cold stress. For this purpose, after soybean (Glycine max) was hydroponically grown for 3 weeks, seedlings were treated with gallic acid (GLA; 1 and 2 mM) and cold stress (5°C and 10°C) and GLA and stress combination for 72 h. The inhibition in growth, water content (RWC), osmotic potential (Ψп) and photosynthetic activity observed under stress and was more at the lowest temperature. Stress also elicited the accumulation of proline (Pro) only at 5°C. While the capacity to maintain high growth, RWC, Ψп and photosynthetic efficiency was observed in GLA-treated plants under stress, Pro accumulation could not achieve with GLA plus stress. Any increase in total activities of superoxide dismutase (SOD) and catalase (CAT) induced by stress treatments determined. The lower cold stress caused an increase in the activities of ascorbate peroxidase (APX), glutathione reductase (GR) and NADPH oxidase (NOX). GLA treatment under stress (especially at 5°C) could supply the increased activities of SOD, CAT, APX and GR. Also, exogenous GLA application to stress-treated plants increased the enzyme activities in ascorbate-glutathione cycle such as monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) and, contents of ascorbate (AsA) and glutathione. After GLA application under stress, it is observed reduction in hydrogen peroxide (H2O2) and the levels of lipid peroxidation (TBARS), and induction of hydroxyl radical (OH●) scavenging. Our results suggest that GLA is a potent inducer for induction of the scavenging activity of radicals as well as effectively usage of water status and photosynthetic capacity.