This experiment was conducted to improve the method of iodimetry for the determination of cysteamine hydrochloride (CSH) in diet,digesta,and excreta,which will be used to assay the CSH for evaluating the releasing process of encapsulated cysteamine in gastro-intestine of animal.Experiment 1 was to examine the linear relationship between iodine consumption on the amount of CSH with the iodimetry.Six levels of 28.28,113.12,226.24,339.36,452.48,565.61 mg of CSH was adopted in a single-factor completely randomized design.Experiment 2 was to investigate the effect of pretreatment on eliminating interference from diet,digesta and excreta in the determination of CSH with iodimetry.Fifteen samples were composed that in each 2 g of diet,duodenal digesta,jejunaldigesta,ilealdigesta or excreta of chicken,the amounts of CSH (reagent grade) were 30,100 and 300 mg.The volume of 0.1,0.5 or 1 mL of 6 mol/L sulphuric acid solution was adopted in single-factor completely randomized design to pretreat each sample.Experiment 3 was to test the differences between conventional iodimetry and the improved method established in the experiment 2 to determine CSH in diet,digesta and excreta.The amounts of CSH (provided by the encapsulated product) of 28.73,84.84,141.47 and 200.56 mg were mixed in each 2 g of diets,duodenal digesta,jejunaldigesta,ilealdigesta,and excreta of chicken.A two-sample experimental design was adopted to compare 2 methods to determine the content of CSH.The results showed as follows:①There was a significant linear relationship between the iodine consumption or the determined CSH on actual amount of CSH (P<0.01,R2=0.9999);② In the diet mixed with CSH,sulfuric acid pretreatment for iodimetry made the regression of determined on actual amount of CSH consistent with Y=X (P>0.05).In the duodenal or ilealdigesta mixed with CSH,sulfuric acid pretreatment for iodimetry didn't made the regression of determined on actual amount of CSH consistent with Y=X (P<0.05),however,the pretreatment with 0.5 or 1 mL sulfuric acid made the determinred value closer to the actual value than the pretreatment with 0.1 mL.In the jejunaldigesta or excreta mixed with CSH,sulfuric acid pretreatment made the regression of determined on actual amount of CSH consistent with Y=X (P>0.05),whereas,the pretreatment with 0.1 mL sulfuric acid made the determined value significantly lower than actual value of CSH (P<0.01).③In diet,duodenal,ileal and jejunaldigesta or excreta mixed with CSH,conventional method made the regression of determined on actual amount of CSH deviate from Y=X (P<0.05),whereas,pretreatment with 1.0 mL sulfuric acid made the regression of determined on actual amount of CSH consistent with Y=X (P>0.05).In conclusion,pretreatment with an appropriate amount of sulphuric acid solution cculd improve the determination of CSH by eliminating the interference from diet,digesta or excreta.