A new series of indole-isoxazolone hybrids bearing substituted amide, substituted [(1,2,3-triazol-4-yl)methoxy]methyl group or substituted benzylic ether at position-2 of the indole nucleus was synthesised using a facile synthetic route and the molecules were characterised using spectroscopic techniques. The molecules were screened against three human cancer cell lines to evaluate their in vitro cytotoxic property. Most of the trifluoromethyl substituted derivatives exhibited better growth inhibition activity than their methyl substituted analogues. The SIRT1 inhibition activity of two potent molecules (I17 and I18) was investigated and the SIRT1 IC50 values are 35.25 and 37.36 μM, respectively for I17 and I18. The molecular docking studies with SIRT1 enzyme revealed favourable interactions of the molecule I17 with the amino acids constituting the receptor enzyme.