ABSTRACT. – Isolation trials from various tomato-growing sites in Kafrelsheikh governorate showing characteristic symptoms of wilt yielded one fungal isolate which was purified and identified as Fusarium solani. In vitro study, the synthetization of silver nanoparticles by Mentha spicata leaf extract was subjected to physical characterization using scanning electron microscopy (SEM) images, which confirmed that the particle diameters of silver nanoparticles (AgNPs) ranged from 57 to 97 nanometers. The antifungal activity of synthesized AgNPs with poisoned food technique was used against a pathogenic fungus with different concentrations (50, 100, 150, and 200 mg/l); furthermore, different concentrations of the fungicide Vitavax (0.5, 1.0, 1.5, and 2.0 g/l) and two biological control agents (Trichoderma harzianum, Bacillus subtilis) were also applied to investigate their antifungal activity against the fungus. The pots experiment was applied under greenhouse conditions during the 2020 season by soaking tomato seedlings in different treatments. The results indicated that the AgNPs treatment yielded the least disease severity among various treatments. All treatments were found effective at different rates, in particular, AgNPs to promote the vegetative growth parameters of tomato plants and controlling the root rot disease caused by pathogenic fungus. Treated plants with AgNPs recorded a low concentration of proline and the highest values of chlorophyll pigments. Furthermore, AgNPs improved the anatomical measurements compared with infected plants without treatment. This study demonstrated the biosynthesis of AgNPs by Mentha spicata leaves extract, which proved a distinct fungicidal activity against pathogenic fungus.