Abstract: Chemical Oxygen Demand (COD) is an important parameter in water-pollution control analysis. COD often is used as a measurement of pollutants in wastewater and natural waters. The objective of this research was to compare the standard method (open reflux method) and ISO, 6060 method in COD measurement of standard solutions and water and wastewater samples. Solutions of KHP (Potassium hydrogen phthalate) with a theoretical COD of 500 and 1000 mg O2L-1 were used as stock standards. The COD values of standard solutions were determined by the standard method and ISO 6060 (1989) method. After comparison between two method results showed that there is significant difference (p< 0.05) only for two concentration (ThOD= 100,400 mg L-1). Both ISO 6060 method and standard method (open reflux method, 5220B) were used to determine the COD values of a variety of water and wastewater samples. Based on average of data from twice measurement, they showed agreeable results which obtained from both methods.