Electromagnetic waves affect living organisms and it is of great interest for wide interaction of new sources with a diversity of frequencies and powers to life of people. In the last few years, many authors have proposed that the biological effect of electromagnetic fields in both the high-frequency and low-frequency ranges are connected with oxidative processes in tissues. Studying the changes in redox balance, we could examine this idea. In the present work, we tried to elucidate how oxidant/antioxidant status in brain tissues responds to chronic irradiation by decimeter microwaves in rats. For this purpose, 460 MHz microwaves were used for whole body irradiation of rats at the power densities less than 0,1 mW/cm2 that are considered to be athermal. The levels of total thiols and easily accessible thiols, activity rate of antioxidant enzymes gluthatione reductase, superoxide dismutase, gluthatione peroxidase and thioredoxin reductase were measured in the tissues of visual cortex and hypothalamus of rats exposed to long-term irradiation during 1-4 weeks with a 20 min exposure/day. As an oxidant production index, we used lipid peroxidation product–malondialdehyde. Measurements were carried out in homogenates of tissues and particularly in mitochondrial fraction. The results showed that specific absorption rate (SAR) of 15 mW/kg displayed distinct changes of redox status depending on exposure time. Both ascorbate-dependent and NADPH-dependent induced lipid peroxidation experiments demonstrated the contributions of mitochondrial ETC and NADPH oxidase to oxidant production with following peroxide accumulation during microwave exposure. The studies showed that the changes in redox status of hypothalamus tend to return practically to control level after a 4-week irradiation, but visual cortex redox status remains sufficiently changed. More detailed studies are required to be conducted to determine the physicochemical mechanisms underlying the biological effects of decimeter irradiation.