The camellia tree is widely grown in the Goto Islands, but its leaves are not effectively utilized. We developed a new fermented tea by rolling of camellia and green tea leaves at a ratio of 1 : 9. The tea exhibited good taste and smell. Feeding of a freeze-dried fermented tea extract suppressed elevations in blood glucose level of KK-Ay mice, an animal model of diabetes. In humans, the fermented tea suppressed postprandial glucose levels. Improvement of hyperglycemia is likely due to suppressed glucose absorption via inhibition of intestinal α-glucosidase activity. Sprague-Dawley rats fed a diet containing fermented tea extract had lower white adipose tissue weight, and serum and hepatic triacylglycerol concentrations. These effects were thought to be exerted by decreases in intestinal fat absorption and suppression of hepatic lipogenesis. Thus, the mixed fermented tea appears to exhibit antihyperglycemic and hypotriacylglycerolemic properties. We have successfully commercialized the mixed fermented tea, named “Goto Tsubaki-cha”. We anticipate that this tea will contribute to the revitalization of the local economy and agriculture of the Goto Islands.