Abstract: The use of water extract of Quinoa Seeds Water Extract (QSWE) in the manufacturing of milk-based fermented beverage was investigated. The prepared QSWE was used to replace 0, 25, 50, 75 and 100% of Buffalo Skim Milk (BSM) and these mixtures were used for manufacture of fermented beverages using 2% of yogurt starter. The obtained fermented beverages were stored at 5±1°C for ten days. The changes in the chemical composition, sensory and microbiological quality of the fermented beverages were followed during the storage period. Minerals and amino acids values of fermented beverages were evaluated when fresh. The data showed that, the total solids and carbohydrates contents decreased with increasing the ratio of added QSWE but there were no significant differences in the results of the protein, fat and ash contents between the control and the other treatments during storage. Results showed that the acidity increased in control and all treatments but T3 and T4 treatments had relatively lower acidity than the control during storage. Minerals contents in fermented quinoa beverages were decreased with increasing the added ratio of Quinoa Seeds Water Extract (QSWE). While, the values of iron in all treatments were found to increase with increasing the added ratio of QSWE. In addition, data showed that all amino acids decreased with increasing the added ratio of QSWE except phenylalanine, methionine, histidine and leucine. The results indicated that the total bacterial counts were higher in all fermented beverages after 3 days and slightly decreased at 7 days then decreased to the end of storage period. In addition, data showed that yeast and mould were not detected at fresh and after 3 days then detected after seven days and decreased at ten days in control and all treatments during storage. No growth of coliform was detected in all fermented beverages under study at both fresh and stored treatments. The sensory evaluation of the fermented product indicated that the control T1 and T2 gained the highest score at zero time for flavor, body, texture, color and appearance among all treatments. After 10 days data showed that the highest score was for T4 followed by T3. Therefore, it is possible to produce fermented beverages by adding 75 or 100% quinoa seeds water extract to BSM as alternative to the fermented milk beverages successfully.