Musca domestica is an important mechanical vector of enteric pathogens, and rising insecticide resistance along with the environmental impact of synthetic insecticides have driven interest in plant-based alternatives. This study evaluated the repellency activity of Murraya koenigii (curry leaf) essential oil against M. domestica. A laboratory-based true experimental design tested three delivery formulations: direct essential oil, aromatherapy diffuser, and paraffin-based candle. Essential oil was obtained from fresh curry leaves via steam distillation. Repellency was tested using 25 adult flies per experimental unit, with three independent biological replicates at each of six concentration levels (including control) per formulation, totaling 1,350 flies. Concentration ranges were 3.33-16.67% (direct oil), 0.1-0.5% (diffuser), and 0.2-1.0% (candle). Data were analyzed using one-way ANOVA followed by the LSD test (\alpha = 0.05). All three formulations showed significant, concentration-dependent repellency (direct oil: F(5,12) = 5.718, p = 0.006, \eta^2 = 0.704; diffuser: F(5,12) = 23.489, p < 0.001, \eta^2 = 0.907; candle: F(5,12) = 30.695, p < 0.001, \eta^2 = 0.927). The highest repellency for direct oil and diffuser was both 78.67% (at 16.67% and 0.5%, respectively), while the candle formulation achieved the highest overall repellency at 92.00% (at 1.0% concentration). Under these laboratory conditions, the paraffin-based candle formulation showed the strongest repellent effect among the three delivery systems. These findings suggest that M. koenigii essential oil, particularly in candle form, has practical potential as a low-cost, eco-friendly botanical repellent for household and public-health fly control, pending field validation, exposure standardization, and safety assessment.