To investigate what effects would be brought about on starch saccharification by adding certain monosaccharides, we have given 1.0 cc of 1.0% taka-diastase solution to 2.0% starch solution 5.0 cc; moreover. have conducted some saccharification tests by adding 1/1000, 1/100, 1/10 and 1.0 mol solution of glucose, galactose, fructose or mannose, and obtained the following results. (1) The starch saccharification by taka-diastase has been inhibited by an addition of the above-mentioned monosaccharide; especially, most marked in the case of glucose addition, next, galactose, then fructose and mannose, the last being feeblest of them all. After that, we have paid observations on this inhibition degree as well as on the kind of monosaccharides, in comparison with certain structural formulas ascribed to various saccharides. (2) In case 1/1000 mol solution 1.0 cc (the content of each saccharide is 0.18 mg in all cases) is added, in either case where 1.0% taka-diastase solution 1.0 cc or 2.0% starch solution 5.0 cc is concerned (which is same to the bottom), suffer no effect on its saccharification; yet, it has been inhibited considerably in case 1/10 mol solution 1.0 cc (the content of each monosaccharide 18.00 mg) has been added, and has been inhibited to a great degree in case 1.0 mol solution 1.0 cc (the contenl of each monosaccharide 180.00 mg) has been added; on the other hand, in view to an addition of 1/100 mol solution 1.0 cc (the content of each monosaccharide 1.80 mg) it is thought almost out of question on account of very slight difference it has proved against the controls, which is hard to detect any inhibition. At any rate, from 1/1000 to 1.0 mol solution 1.0 cc, i.e., within the range of from 0.18 to 180.00 mg., as the amount of saccharide added becomes greater, the starch saccharification by taka-diastase has proved more and more to suffer inhibition. (3) The content of glucose, galactose, fructose or mannose in each 1.0 mol solution 10 cc being 180.00 mg, corresponds to 1.83 times the amount of the final product of starch hydrolysis (by Liebermann's method), i.e., 98.22mg.; even if such a comparatively considerable amount of monosaccharicde as this is added, there takes place no inhibition whatever for the early stage of starch saccharification. (4) The inhibition of starch saccharification caused by taka-diastase may be, not only owing to glucose, galactose, fructose or mannose, but also owing to various kinds of intermediate products formed in saccharification solution, which have power to thwart starch saccharification caused by taka-diastase.