Abstract: Sample of fresh garlic was ground into slurry and a definite amount (about 50.00 g) of the slurry was taken and treated with 20 mL of conc.HNO3 to oxidize the sulfoxide in the sample into sulfate ion.The suspension was diluted with water,filtered and made up to a definite volume.An aliquot of the filtrate (ca.1/10) was taken and it acidity adjusted to pH 5-6 with sodium hydroxide solution,and an equal volume of ethanol was added to the solution.Titrate the SO2-4 in the solution with standard lead nitrate titrating solution,using Pb(Ⅱ)-ion selective electrode to indicate the end point,the potential of which was determined by the method of 2nd derivation.RSD′s of this method was shown as 0.44%,and no significant difference were found between the results obtained by this method and by the gravimetric method.