Abstract: Gutzeit's method,Bettendorf's method and Thiele's method are commonly employed in pharmacopoeias for the determination of arsenic.On account of the complicated conditions of Gutzeit's method and the low accuracy of the other two,we conducted a study on the application of heteropoly molybdenum blue method for estimating arsenic in drugs and satisfactory results were obtained. Arsenic in such drugs,as calcium lactate,calcium gluconate,dextrose,sul- fadiazine etc.was determined directly without destructing the organic matter. Drugs containing sulfur reducible by nascent hydrogen to form H₂S,and those containing a very small amount of arsenic require a large quantity of sample, were determined after destruction of the organic matter.Arsenic in antimony- containing drugs was determined after the removal of antimony with pyrogallol, and that in pyridine derivatives was determined directly after oxidation with acid permanganate.The percentage of recovery of arsenic using the wet ashing me- thod was higher than that using the dry ashing method.