The objectives of the study were to investigate the variability of oat (Avena sativa L.) grain physical traits and chemical composition and to determine relationships between traits. Field experiments including five hulled oat genotypes were carried out at the State Stende Cereal Breeding Institute for two seasons during 2010-2011. Variation of traits was mainly determined by genotype (ω2 = 53 - 88%), with the min/max values for 1000 kernel weight 32.4/36.5 g, test weight 470.0/507.9 g·L-1, hull content 215.4/265.6 g·kg-1, crude protein 110.0/124.9 g·kg-1, starch 456.9/483.0 g·kg-1, β-glucans 28.1/36.6 g·kg-1 and crude fat 46.2/60.0 g·kg-1. Oat variety ‘Arta’ had the highest test weight (507 g·L-1) and contents of crude protein (124.9 g·kg-1), β-glucans (36.5 g·kg-1), α-tocopherol (7.8 mg·kg-1), average crude fat (55.5 g·kg-1) and total phenolics (113.9 mg gallic acid equivalents/GAE 100 g-1 DM) in the grain. Expression of traits significantly depended on meteorological conditions in the specific year. In both years of investigation there were significant (p < 0.05) positive correlations between contents of β-glucans and crude fat, and negative correlation of β-glucans with starch content, total phenolics and antiradical scavenging activity.