The aim of the diploma thesis was to assess the influence of foliar application of selenium on the yield and the content of selenium in the oil of rapeseed (Brassica napus) by means of a small plot experiment founded in 2013 on the land of Školní zemědělský podnik Žabčice. The selenium was applied in the form of sodium selenite in two doses of 30 and 60 g of selenium on hectare. The application of both of the two doses was carried out in three periods of time: before flowering, after flowering and in the form of a divided application i.e. half of the dose was applied before flowering and the other half after flowering. The application of selenium did not have statistically important influence on the yield of the seeds of rapeseed. In all the variants there was a statically highly important increase in the content of selenium in the seeds as compared with a control variant. The highest content of selenium was detected with the divided 60 g dose of selenium. Differences in the content of selenium in the seeds between the 30 g dose variant and the 60 g dose variant were not statistically significant. The influence of the time of application of selenium on the total content of selenium in the seeds of rapeseed was statistically highly important. The lowest content of Se in the seeds was observed with the variant to which Se was applied before flowering. Contrastively, the highest content of selenium was detected with the variant with divided application of selenium. The application of selenium negatively influenced oiliness. With all the variants there was an approximately 10 % reduction of oiliness as compared with the control variant to which no selenium was applied. Differences in oiliness caused by the size of the doses of Se and times of applications are not statistically significant.