The corrosion inhibition of mild steel in sulphuric acid by flavonoids, separated from Nypa fruticans Wurmb leaves extract was studied using weight loss technique at 303K, 313K, 323K, 333K and 353K,. The constituents were separated by fractionation using Soxhlet apparatus after room temperature extraction with 70% acetone. The constituents were identified using standard functional group analysis (phytochemical screening) methods. The inhibitor concentrations of 0.1 g/L, 0.2 g/L, 0.3 g/L, 0.4 g/L and 0.5 g/L were used in 0.1M, 0.5M, 1M and 2M concentrations of acid solutions. Inhibition efficiency increased with increase in temperature and inhibitor concentration. Thus, maximum inhibition efficiency of 74.48% was obtained at the optimum temperature (323K) and concentration (0.5 g/L) for the flavonoid constituent. The flavonoid (catechin) separated from Nypa fruticans Wurmb leaves extract were used separately as efficient corrosion inhibitor of mild steel in H2SO4.