Abstract: The root system is vital for plants to grow and develop well. Promoting the initiation of roots will contribute to enhancing the resistance of plants to biotic and abiotic stress. Plant growth regulators as mepiquat chloride (MC) are organic substances that modify the course of physiological processes in plants. The effects of MC application to oilseed rape cv. Bellevue and ES Cesario F1 on the initial growth of the roots were studied in a chamber with controlled environmental conditions. Measurements of total root length, average root diameter and surface area were made using the Smart Root programme. MC had a positive effect on all studied parameters. In comparison to controls, it increased the thickness of the root neck (11% for Bellevue, 13% for ES Cesario F1) as well as the length (4% for Bellevue, 6% for ES Cesario F1), total length (64% for Bellevue, 83% for ES Cesario F1) and volume (68% Bellevue, 86% for ES Cesario F1) of the root system.