Phenolic compounds which occur in red cabbage, have strong antioxidant activity, and can be used as substances protecting human cells from oxidation. Field experiment conducted in the years 2007–2009 in Department of Horticulture at Wroclaw University of Environmental and Life Sciences involved research on the effect of different nitrogen doses on yield, chemical composition and antioxidant activity of red cabbage. Nitrogen, in the form of ammonium saltpeter, was introduced in the following doses: 50 kg N·ha^-1; 150 kg N·ha^-1 and 250 (150+100) kg N·ha^-1. In the third decade of April red cabbage seeds of ‘Langendijker’ cv. were sown into multipots. The seedlings were planted on 5 m² – area plots at the end of May. Harvesting took place in the second week of September, when there was assessed marketable and total yield. In samples of red cabbage heads there were estimated the content of nitrates, vitamin C, total and reducing sugars, polyphenols, anthocyanins, as well as dry matter and soluble solids. In order to investigate antioxidant activity there were applied DPPH and ABTS tests. In experiment optimum nitrogen dose for red cabbage was 150 kg N·ha^-1. The highest amount of anthocyanins were determined in the leaves of red cabbage fertilized with moderate N dose up 150 kg N·ha^-1. The highest antioxidant activity proved to characterize edible parts of red cabbage fertilized with nitrogen in the dose of 50 kg N·ha^-1, while the level of total polyphenols featured the lowest values in the conditions of intensive nitrogen fertilization amounting 250 kg N·ha^-1.

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