A series of novel 3-tert-butyl-7-(aryloxymethyl)-4H-[1,3,4]thiadiazolo[2,3-c][1,2,4]triazin-4-ones (5a-5n) were synthesized by refluxing 3,3-dimethyl-2-oxobutanoic acid (trimethyl pyruvic acid) (1) and thiocarbohydrazide (2) in ethanol as solvent for 12 h, to yield 3-mercapto-4-amino-6-tert-butyl-1,2,4-triazine-5(4H)-one (3) (Scheme 1), then the compound (3) was condensed with different substituted aryloxyacetic acids (4) in POCl3 at 90 °C for 8 h (Scheme 2). The structures of the newly synthesized compounds were confirmed by IR, (1)H NMR, (13)C NMR, elemental analyses and mass spectroscopic studies. Few of the synthesized compounds exhibited moderate mosquito-larvicidal and antibacterial activities. Among the novel derivatives, the compound (5f) showed relatively high larvicidal activity against a malaria vector. Compounds (5i) and (5m) exhibited a broad spectrum antibacterial activity against Gram positive and Gram negative species and hence they may be considered as drug candidates for bacterial pathogens.