4-[Arylidene-amino]-3-thiophen-2-ylmethyl-4,5-dihydro[1,2,4]triazole-5-one compounds (3a-g) with Schiff base character were obtained from the reaction of 4-amino-3-thiophen-2-ylmethyl-4,5-dihydro-1H-[1,2,4]triazole-5-one (2) with various aldehydes. 1-(2-Oxo-2-phenyl-ethyl)-4-[arylidene-amino]-3-thiophen-2-ylmethyl-4,5-dihydro-1H-[1,2,4]triazole-5-ones (4a-g) were synthesized from the reaction of corresponding compounds 3a-g with bromoacetophenone. 1-(2-Hydroxy-2-phenyl-ethyl)-3-thiophen-2-ylmethyl-4-[aryl-amino]4,5-dihydro-1H-[1,2,4]triazole-5-ones (5a-g) and 1-(2-hydroxy- 2-phenyl-ethyl)-3-thiophen-2-ylmethyl-4-[arylidene-amino]4,5-dihydro-1H-[1,2,4]triazole-5-ones (6b,d,e) were obtained from the selective reduction of 1-(2-oxo-2-phenylethyl)-4-[arylidene-amino]-3-thiophen-2ylmethyl-4,5-dihydro-1H-[1,2,4]triazole-5-ones (4) with NaBH(4). They were characterized by IR, (1)H-NMR, (13)C-NMR, and elemental analyses. Compounds 2, 3a, 3c, 3g, 4f, 5b, and 5g showed good antifungal activity against yeast-like fungi. Compounds selected by the National Cancer Institute (NCI, USA) were investigated for antitumor activity.