An accurate, sensitive and selective method for the determination of Natulan is proposed. The method is based on the oxidation of Natulan with 0.1 N ammonium cerium(IV) sulphate solution to formaldehyde and N-isopropyl benzamide-4-carboxaldehyde. The latter is separated as its 2,4-dinitrophenyl-hydrazone, which, when treated with ethanolic potassium hydroxide solution, gives a wine red colour. The method is applicable to microgram amounts and can be used successfully in the determination of Natulan in capsules. The stoicheiometry of 1 mol of Natulan to 6 mol of cerium(IV) has been shown through a titrimetric study.