Abstract: An improved circular system of small intestine in rats was used for investigateabsorption of SMZ in relation to O/W partition coefficient under different pH.Theresults which revealed a half-logarithm relationship between partition coefficient and absorption were as follows absorption rate; 39.35% at pH4, 28.13% at pH6, 5.6% at pH8; absorption rate constants: 0.396 h^-1 at pH4, 0.303 h^-1 at pH6, 0.057h^—1 at pH8; Half—life of absorption: 1.76 h at pH 4, 2.29 h at pH 6, 16.00 h at pH 8.