Poststroke depression, the second most serious psychosomatic complication after brain stroke, leads to delay of the rehabilitation process and is associated with an increased disability and cognitive impairment along with increase in term mortality. Research into the biochemical changes in depression is still insufficiently described. The aim of our study was therefore to evaluate the possible association between plasma protein oxidative/nitrative damages and the development of poststroke depression. We evaluated oxidative/nitrative modifications of specific proteins by measurement of 3-nitrotyrosine and carbonyl groups levels using ELISA test. Additionally, we checked differences in proteins thiol groups by spectrophotometric assay based on reaction between DTNB and thiols. We also evaluated catalase activity in erythrocytes measured as ability to decompose H2O2. Correlation analysis was performed using Spearman's rank. We observed significant (P < 0.001) differences in all oxidative/nitrative stress parameters in brain stroke patients compared to healthy group. Our research shows that oxidative damage of proteins is correlated with the degree of poststroke depression, while nitrative changes do not show any relationship. We demonstrate a positive correlation between the concentration of carbonyl groups and the Geriatric Depression Scale and a negative correlation between the degree of depression and the concentration of -SH groups or catalase activity.