In the paper, the results were presented of a three-year field experiment carried out during 2007 – 2009, at a Scientific Research Station in Krasne near Rzeszów. The objective of the investigations was to determine the response of oat plants (strains: STH 7105, STH 5417, and STH 7505, a hull-less form) to the application of growth retardant in the form of a Cycocel suspension (CCC) used at various growth phases, such as 13 BBCH, 32 BBCH, and 39 BBCH. The oat plants were sprayed with a CCC suspension, its dosage was 2 l /Ha. No growth retardant was used in the control plots. Based on the investigations performed, no impact of CCC on the vegetation course of oats was found. The statistical analysis accomplished showed that this preparation did not differentiate significantly the yield and mass of 1000 grains. However, the CCC growth retardant had a significant effect on such yield components as stalk length, and number of ears and grains per panicle. The action of this preparation caused the oat plants to become shorter (by 3.5 % on average) and the number of ears and grains to increase by ca. 4.2 % if compared with the control sample of plants. Furthermore, the application of CCC caused the content of protein and fat to increase. However, it did not differentiate the content of fibre and mineral compounds in the form of ash in the oat strains investigated.