In recent years, the effects of electromagnetic radiation (EMR) on living systems have became the subject of frequent investigations. It is believed that EMR is possessed by significant biological activity and can cause metabolic disturbances of the nervous, cardiovascular, immune and other systems, to increase the risk of tumors. However, the mechanisms of biological effects of electromagnetic radiation are still poorly understood. One of the most important factors in the mechanism of biological effects of electromagnetic radiation may be their effect on free radical processes. There is a theory on the impact of electromagnetic radiation on the rate of reactions that take place through a stage of interaction of a pair of paramagnetic particles, in particular, free radicals. This mechanism may be mediated by a free radical chain process including lipid peroxidation (LPO). The deepening of the oxidation processes leads to the formation of carbonyl derivatives of proteins, which are markers of oxidative damage of the latter. Until recently, the study of oxidatively damaged proteins in organism has mostly been characterized as theoretical question. In some studies, this process was considered as a cause of enzyme inactivation, changes in the conformational structure of proteins during oxidative stress. In this paper, we studied the changes in the protein carbonyl levels in rats chronically exposed to 460 MHz electromagnetic radiation up to 14 days (daily for 20 minutes at a power density 30 mW/cm2 and 10 mW/cm2). The concentration of carbonyl derivatives was determined by the method of Dubinina et al. (1995). Results show that the content of carbonyl proteins in both plasma and serum is increased compared with the control animals, and this increase is more significant in the serum. It has also showed that the ratio of carbonyl content in serum and plasma becomes higher for the irradiated organism. Greater increase of carbonyl groups in serum versus plasma, apparently, can be explained by the ability of fibrinogen to scavenge free radicals. In the absence of fibrinogen, oxidative modification of other proteins may proceed more intensely leading to an increase in the serum carbonyl groups level.