The effects of ginseng saponin and its related materials on aflatoxin production by Aspergillus parasiticus NRRL2999 in yeast extract sucrose (YES) medium were studied. Maximal production of aflatoxins by the mold in the medium occurred after 9 days at $28^{circ}C$. When various concentrations of ginseng saponin were added to the medium aflatoxin productions were significantly reduced (p<0.05) compared to the control after 9 days at $28^{circ}C$. 0.05% of saponin in the medium greatly decreased aflatoxin synthesis, and no aflatoxins were synthesized by the mold in the medium contained 5.0% of saponin. When various concentrations of saponin diol and triol were added to the medium both ingibitory and sitimulatory effects on alfatoxin production were resulted. Saponin fraction numbers of 1, 2, 4, 5 and 6 decreased aflatoxin production, however the numbers of 3 and 7 stimulated the toxin production. 0.05% of adenosine, guanosine, caffeine and xanthosine in the media inhibited aflatoxin production (p<0.05), but adenine and cytosine increased the production. When 5.0% of saponin was added to the medium aflatoxins were not synthesized at all, but total lipid synthesis and mold growth were highly stimulated. Both the synthesis of total lipid and mold growth were reduced in case of aflatoxin synthesis stimulated.