ABSTRACT In order to reduce the excessive reliance on the toxic chemical fungicides, the present study aimed to isolate the total potato glycoalkaloids (TPAs), and the two steroidal alkaloids α-chaconine and α-solanine from potatoes, Solanum tuberosum L. Their structures were characterized using physical and spectroscopic methods including (UV, IR, 1H, 13C--NMR, 2D 1H-1H COSY, HMBC and NOESY). Silver nanoparticles (AgNPs) were prepared from potato alkaloids through a green synthesis approach. Potato alkaloids and their nanoparticles inhibited mycelial growth of the phytopathogenic fungi Alternaria alternate, Rhizoctonia solani, Botrytis cinerea and Fusarium oxysporum f. sp. lycopersici with low minimal inhibitory and minimal fungicidal concentrations. R. solani was the most susceptible, while F. oxysporum was the most resistant. TPAs was the most fungitoxic (EC50's were 19.8, 22.5, 26.5 and 32.3 µg/ml against R. solani, A. alternate, B. cinerea and F. oxysporum respectively). A mixture of α-solanine and α-chaconine (1:1) showed a marked antifungal activity. AgNPs (size 39.5-80.3 diameter) from alkaloids showed improved fungitoxic activity (EC50's of TPAs nanoparticles ranged between 10.9 and 16.1 µg/ml). Alkaloids exhibited no or a slight phytotoxicity against wheat and radish. Results recommend the potential of using potato alkaloids and their nanoparticles as biorational alternatives to conventional fungicides.