The experimental work was conducted during the two successive seasons of 2018/2019 and 2019/2020 at the Experimental Farm of Ismailia Agriculture Research Station, Ismailia Governorate Egypt, to study the effect of zinc nanoparticles as foliar spray (0.25, 0.50 and 1.0 g/l, beside unsprayed (control treatment)) on growth, seed yield and active constituents of Silybum marianum L. The experiment was designed as randomized complete blocks design with three replicates. As for the response of Silybum marianum L. plants to foliar application with zinc nanoparticles, results indicated that, treating Silybum marianum L. with ZnO-NPs at 1 g/l as foliar spray increased plant height, number of leaves/plant, number of inflorescences/plant, stem diameter, root length, number of roots/plant, dry weight of roots, herb and inflorescences/plant, chlorophyll a, chlorophyll b and total chlorophyll (a+b), seed yield /feddan., N, P and K contents in leaves and Zn concentrations in fruits, TXF, SDN, SBN, SCN, ISBN and total silymarin in fruits, in both seasons.