A new class of isoxazole derivatives containing 1,2,4-triazole moiety were synthesized to meet structural requirements essential for antibacterial, antimycobacterial and anticancer activity. 1-(3,5-dipheny-1H-1,2,4-triazole-1-yl) ethanone ( compound 2) was treated with different aromatic aldehydes to get substituted chalcones (3a-g) then subsequently cyclized with hydroxyl amine hydrochloride to yield 1-[5-(substituted aryl)-1,2-oxazol-3-yl]3,5- diphenyl-1H-1,2,4-triazoles (4a-g). IR, H-1-NMR, Mass spectra and elemental analysis were recorded to confirm the structures of target compounds. Compound 3a-g and 4a-g were screened for in vitro antimicrobial activity against B. subtillis NCIM 2063, E. coli NCIM 2065, C. albicans NCIM 3471 and A. niger NCIM 1196. MIC values were determined by liquid broth method. Chloro, nitro, methoxy substituted derivatives exhibited significant antibacterial and fungicidal potential. The in vitro antimycobacterial activity of the compounds 4a- g against Mycobacterium tuberculosis H37Rv was evaluated. The highest inhibition was observed through compound 4f as 76% at > 6.25 mu g/ml. Among the synthesized isoxazole derivatives, five compounds have been selected and evaluated for their anticancer activity at the National Cancer Institute for testing against a panel of approximately 60 different human tumor cell lines derived from nine neoplastic cancer types. The most efficient anticancer compound 4e was found to be active with selective influence on leukemia cancer cell lines, especially on SR with a growth % of 71.72.