The aim of the study was to determine the response of new cultivars of spring barley in terms of the grain yield, yield components and protein content in grains, to an increase in the sowing rate. Microplot experiments were carried out in the IUNG-PIB experimental plot in Puławy, where the influence of the following sowing densities on the yielding of selected cultivars was studied: 250, 350 and 450 grains m-2. In the years 2011–2012, the following cultivars were investigated: Basic, Goodluck, Iron, KWS Olof, Natasia, and in the years 2012–2013 cultivars: Despina, Ella, Fariba, Gawrosz (hulless variety), Kucyk and Raskud. The experiments were carried out on a soil of a good wheat complex (heavy loamy sand deposited on light loam). An increase in grain yield (averaged across cultivars) was obtained as the sowing density was increased up to 450 grains m-2. At a high sowing rate (450 grains m-2), a significant increase in the grain yield of the following cultivars occurred: Basic, Iron, Despina and Gawrosz, and an increase in the yielding of other cultivars at this sowing rate, compared to the sowing rate of 350 grains m-2, constituted a trend. The largest increases in the yield at a high sowing rate, in comparison to the low rate in the first series of experiments (2011–2012), were demonstrated by the following varieties: Iron (29%), Basic (25%) and Goodluck (21%), and smaller increases were noted for the cultivars: KWS Olof (13%) and Natasia (10%). In the second series (2012–2013), higher yields at a high sowing rate, as opposed to a low sowing rate, were demonstrated by the following cultivars: Gawrosz, Raskud and Despina (31–34%), and lower yields by: Ella, Fariba and Kucyk cultivars (19–21%). The increase in grain yield at a high sowing rate was the result of a bigger number of ears per unit of area in all cultivars (especially in the Basic and Raskud cultivars). The difference in the weight of 1000 grains and the number of grains per ear of the investigated varieties as a consequence of the sowing rate was negligible. In the years 2012–2013, there occurred an increase in the protein content of grains at a high sowing rate. Among all the cultivars (on average considering the sowing rate), the highest grain yields were produced by Iron and Ella, the highest density of the number of ears per unit of area was demonstrated by Natasia, Kucyk and Ella. The cultivars Iron, Gawrosz and Raskud were found to have a significantly higher number of grains per ear than the remaining cultivars.