Naja sumatrana is the dominant cobra species in Malaysia, Singapore, Borneo, and Sumatra, and it does not have specic antivenom.  e Ha ine antivenom has been advocated instead.  is study aims to determine the ecacy of this antivenom against Naja sumatrana envenoming using a mouse model. Methods. Male Swiss albino mice were used. Intravenous LD50 was rst determined separately for Naja naja and Naja sumatrana venom. ED50 was determined by preincubating antivenom with each venom at 2.5 LD50 before administering the mixture into the tail vein. Validation was carried out using a challenge test. Each mouse received 111 g of Naja sumatrana venom intramuscularly followed by intraperitoneal administration of dilute Ha ine antivenom. Survival was recorded 24 hours aer envenoming. Results.  e LD50 of Naja naja venom was 78.13 g, standard error (SE) 13.3 g.  e ED50 of the Ha ine antivenom against Naja naja venom was 45.9 mg, SE 7.5 mg.  e LD50 and ED50 of Naja sumatrana venom were 55.5 g, SE 12.0 g; and 73.9 mg, SE 12.0 mg, respectively.  e intra-peritoneal ED50 against 111 g intramuscular Naja sumatrana venom was 136.95 mg, SE 36.74 mg. Conclusion.  e Ha ine polyvalent antivenom exhibited cross-neutralisation against Naja sumatrana venom when used at a higher dose.