The aim of the study was to explore quality of coix seed grown in Xingren, Guizhou (China) during storage. The results indicated that, color, ordor, main contents and correlate indexs of coix seed changed significantly during storage, which reflect the quality of coix seed decreases. Results: the color of coix seed changed with storing time lengthening. Original milky white, glossy coix seed became dimmed with yellowish and grayish with storing period lengthens. The odor was also from the original sweet aroma, which was ultimate rancidity. The rancidity of coix seed bacame stronger with storing time lengthening. During storage period, there was no significant difference in protein, starch and ash contents, but moisture content declined gradually (decreaesd 37.06%), fat content reduced obviously (reduced 15.00%). Fatty acid value, peroxide value, electric conductivity, malondialdehyde and reducing sugar content of coix seed increased with storing time lengthening, and increased 272.56%, 416.21%, 123.78%, 99.91% and 5.83%, respectively. While, the acidity and lipase activity increased at first and then decreased. The fatty oxidation of coix seed was the main cause of the decrease in quality.Changes in fatty acid value, peroxidation value, malondialdehyde content, lipase activity and electric conductivity sensitively reflect the fat oxidation of coix seed with storing period lengthens, and reflect the decline of coix seed quality.