Erythrina variegata L. (dedap), from the Fabaceae family, has been widely used as an anti-inflammatory, antimicrobial, antioxidant and wound healing agent. There is a lack of literature data regarding the optimisation of extraction parameters from this plant on antioxidant activities, particularly involving Ultrasound-assisted Extraction (UAE). Therefore, this study aims to determine the optimum extraction parameter for the UAE technique from E. variegata leaves extracts on in-vitro antioxidant activities by applying a multi-level factorial design. The solvent (methanol) concentration (X1) and extraction time (X2) were the independent variables, while the dependent variables are antioxidant assays: DPPH radical scavenging activity (Y1), ferric reducing antioxidant power (FRAP) (Y2) and total phenolic content (TPC) (Y3). The results showed that the optimised extraction condition was at 100% solvent concentration and 60 minutes of extraction time, which demonstrated 0.301 ± 0.013 mg/mL, 54.624 ± 0.143 mg FeSO4/g and 29.433 ± 0.062 mg GAE/g of DPPH activity, FRAP assay and TPC values, respectively. However, the highest extraction yield of 18.56% was obtained when extracted at only 25% solvent concentration and 60 minutes. This research has provided basic scientific evidence that optimum UAE conditions for E. variegata are crucial to maximising antioxidant activity.