A field experiment was conducted on a Haplic Podzol (PZha) during the period 2012–2014. The aim of this study was to evaluate the grain chemical composition of winter rye grown on a biochar-amended soil. The following grain quality traits were determined: content of N, P, K, Mg, Ca, Cu, Zn, Mn, Fe and B, total protein content (TPC), total starch content (TSC), reducing sugar content (RSC), phenolic content (PhC), flavonoid content (FC), chelating power (ChP) and reducing power (RP). Biochar was applied once before sowing winter rye in 2011 at three rates: 10 Mg ha-1 (BC10), 20 Mg ha-1 (BC20) and 30 Mg ha-1 (BC30). The biochar was pyrolyzed from wheat straw at 350–650°C. Rye grain was evaluated each year after harvest, i.e. 12, 24 and 36 months after biochar application to the soil. At all assessment times, the N content in rye grain from the biochar-amended treatments was higher than in the control treatment (BC0). In the first year of the study, the lowest P content (3.40 g kg-1) was determined in grain from the treatment BC30, while in the third year in the treatment BC10 (3.31 g kg-1). At the second and third assessment times, the content of K, Mg and Zn in grain from the biochar-amended treatments decreased with increasing biochar rate, whereas the Mn content increased. In the treatment BC30, at the first assessment time the grain Ca content was found to be lowest (0.147 g kg-1), while after 36 months it was highest (0.302 g kg-1). In the first and third years of the study, the Cu content in the treatment BC30 was higher than in the BC10 (by 31.6% and 57.3%, respectively). At the second and third assessment times 24 and 36 months after biochar application, the Fe and B content in grain obtained from the treatments BC10 and BC20 was higher than in that harvested from the BC30 plots. In grain harvested from the plots where 20 Mg ha-1 biochar had been applied, the total protein content and total starch content were found to be higher than in grain from the plots where 30 Mg ha-1 had been applied (by 10.7% and 17.1%, respectively). The highest reducing sugar content (9.02 mg g-1 dry weight (DW)) and phenolic content (6.8 mg of gallic acid equivalent (GAE) g-1 DW) were determined in rye grain from the BC10 plots. Soil amendment at different biochar rates did not have an unambiguous effect on the antioxidant capacity parameters (chelating power and reducing power) of rye grains.