Abstarct: A rapid, simple and accurate spectrophotometric method is proposed for the determination of hydrazine and phenyl hydrazine. The method is baxsed on the reaction of hydrazine and phenyl hydrazine with produced iodine has been result of iodide and periodate the remaind iodine has reacted with methylene green and make it colorless. The reaction was monitored spectrophotometrically at 613 nm. Under the optimum conditions, hydrazine and phenyl hydrazine could be determined in the concentration range of 0.030-0.35 micro-g/mland 0.10-1.1 micro-g/mlrespectively. The detection limit of the method is 0.0279 micro-g/mlfor hydrazine and 0.0914 micro-g/mlfor phenyl hydrazine. The relative standard deviations for 6 replicated determinations of 0.050, 0.090, 0.10 and 0.350 micro-g/mlhydrazine are 12.5%, 7.1% 6.3% and 3.5%, respectively and The relative standard deviations for 6 replicated determinations of 0.20, 0.70 and 0.90 micro-g/mlphenyl hydrazine are 9.9%, 2.6% and 4.1%, respectively. Interferences due to foreign ions are studied and the method is applied for the determination of hydrazine and phenyl hydrazine in water samples.