Abstarct: A simple, sensitive, and selective kinetic spectrophotometric method with no need for removing interfering substances is proposed for determination of thiocyanate ion in water, wastewater, mouthwash, and biological samples. The method is baxsed upon the inhibiting effect of the thiocyanate on the reaction between sodium bromate and methyl red in acidic medium. The decolorization of methyl red was used to monitor the reaction spectrophotometrically at 518 nm. Thiocyanate can be determined in the range of 0.01-0.20 µg ml-1 with 3σ detection limit of 1 ng ml-1. The relative standard deviations for 6 replicated determinations of 0.05, 0.12, and 0.18 µg ml-1 thiocyanate were 4.2, 2.6, and 1.5%, respectively. The method was successfully used to determine the thiocyanate content of spiked water, wastewater, mouthwash, and biological samples. A rapid, simple, accurate, and high selectively spectrophotometric method is proposed for the determination of periodate in solution samples. The method is baxsed on the reaction of methylene green with periodate in the presence of iodide. The absorbance decrease of methylene green was used to monitor the reaction spectrophotometrically at 613 nm. Under the optimum conditions, periodate could be determined in the concentration ranges of 0.20–6.0 g/mL. The 3σ detection limit of the method is 0.011 µg/ml. The influence of various foreign species was studied and iodate did not interfere over than 200- fold of periodate. The relative standard deviations for six replicate determinations of 0.30, 1.5, 4.0 and 5.5 g/mL of periodate were 3.37, 1.34, 0.50 and 0.55% respectively. The proposed method was applied to the determination of periodate in water samples. Also this method was applied to the indirect determination of ethylene glycol in antifreeze and glycerol in olive oil via malaprade reaction system. The satisfactory results were obtained.