Siddha system of medicine is the main traditional medicine which is very popular in south India and north and east Sri Lanka. In this system herbal, mineral and metal are mainly use for the medicine preparation and to treat the diseases. Each and every part of the herbs can be used for various, multiple ailments because of their different phyto constituents. In Siddha medicine system has been classified into Aga marunthu (Internal) and Pura marunthu (External) having 32 forms of medicines in each. The external remedies are very useful for topical ulcers, skin diseases like eczema, psoriasis bacterial and fungal infections. The purpose this study was Evaluate the efficacy of Antibacterial activity of aqueous extract of Nigella sativa seeds powder against Staphylococcus aureus by used disk diffusion method. The result has been evaluated as the diameter of the zone of inhibition of microbial growth showed that the different concentration (100%, 50%, 25%) of Nigella sativa seed powder's aqueous extract more effective against Staphylococcus aureus. Mean value of the hot extract 100%, 50%, 25% respectively 12.19±1.91mm, 7.63±2.32 mm and 3.78±1.73mm and the mean value of Cold extract were 9.45±1.32mm, 4.21±0.92mm and 2.71±.64mm. Standard maintained 18mm of zone of inhibition. Among, the hot and cold extract, 100% of hot extract was showed more significant affect against Staphylococcus aureus which was 12.19mm. Finally, this study was concluded that the Nigella seeds powder can be used as an antibacterial agent.