Natural Killer (NK) cell has the capability to immunosensitize and cell-mediated lysis of many types of cancer cells, however, most of the cancer cells are evading the NK cell-mediated lysis by down-regulating the NK cell specific ligands. In the present study, we have evaluated the comparative and synergic effect of spironolactone (SPIR) and avemar (AVE) in enhancing the susceptibility of osteosarcoma cells (MG-63) to NK cell-mediated lysis in vitro. The NK cells used in this study was characterised by the expression of CD56 and NKG2D using flow cytometry. At an optimized concentration, SPIR (60 μM) and AVE (5 mg/ml) treatment showed significant upregulation of the NK cell-specific NKG2D ligands (MICA, MICB, ULP1, and ULP2) on MG-63 cells compared to those in untreated group. To evaluate the NK cell sensitisation towards osteosarcoma cells, MG-63 cells were treated with and without SPIR and AVE for 72 hrs, followed by co-culturing with NK cells [different target and effector ratio (E:T), 1:1, 1:2, 1:5, 1:10 and 1:20] for different time periods (4 and 24 hrs). Cytotoxicity analysis reveals that AVE and AVE+SPIR combination treated MG-63 cells are more susceptible to NK cell-mediated lysis than those SPIR treated in time and dose (E: T ratio) dependent manner. In conclusion, SPIR and AVE are potentially enhancing the NK cell mediate lysis of osteosarcoma cells by unregulated the NK cell specific ligands.