A precise analytical assay was developed and validated for the determination of Pacific oyster glycogen using ion chromatography. The Pacific oyster glycogen was quantified by the determination of glucose-6-phosphate (Glc-6-P), which was derived from glucose that was hydrolyzed from glycogen. Glc-6-P, adenosine triphosphate, and adenosine diphosphate were separated by ion chromatography. The method was validated over the curve range 0.5-100mg/L for the abovementioned analytes. The recoveries were between 95% and 102%. The relative standard deviations (RSDs, c=10mg/L, n=9) were less than 4.37%. Unlike a traditional method, this validated method was inexpensive and stable.