The aim of the study was to determine the effect of soil contamination with diesel oil on the early development of three species of the Fabaceae family (Medicago lupulina L., Lotus corniculatus L., Trifolium repens L.). These species have a wide ecological range and they often occur on extensively used lawns. For these reasons, the knowledge on their tolerance to soil pollution with diesel oil can be of great importance in the creative breeding of these plant species cultivars and their seed production for establishing the greenery of communication routes. The studies were carried out under controlled laboratory conditions. The soil substrates were composed of the loamy sand mixed with diesel oil in an amount of 2.5 g and 5.0 g per 1 kg of absolute dry mass of soil. The germination dynamics were analyzed. The measurements were conducted twice a day for 12 days after sowing. The development of seedlings was determined on the basis of the length, diameter, area and volume of the radicle. These features were determined on 20-day-old seedlings of the tested species. For the analysis of plant material, the technique of the scanned image was used in the "WinRhizo PRO 2009" software. It was proven that the tested species have various tolerances for the petrol oil in the soil and demonstrate various defence mechanisms under the stress conditions. The least changes of the seed germination rate on the soil with diesel oil against the control were indicated for L. corniculatus. The defense strategy of that species relied on the radicle development through increasing the diameter and – in consequence – the surface and the volume. M. lupulina also showed good germination capacity in the presence of diesel oil, but the radicle was shorter in comparison to the control. The germination rate of T. repens in the contaminated soil was significantly reduced. The recommendation for using not only L. corniculatus, but also M. lupulina on the contaminated areas should be taken into consideration.