The aim of this research was to examine the effect of harvesting age towards the quantity and quality of the Gambyong variety cassava in Ponjong Subdistrict, Gunungkidul Regency. This research was conducted in Ponjong Subdistrict, Gunungkidul Regency, Yogyakarta Province, Research and Postharvest Laboratory of Agriculture Faculty, Universitas Muhammadiyah Yogyakarta from November 2017 until August 2018. The experiment was done by using field experimental method with a single factor arranged by Randomized Complete Block Design (RCBD). The treatment tested was harvest age which consisted of 6 treatments, namely harvest age of 4, 5, 6, 7, 8 and 9 months. The parameters of the observations consisted of plant height, number of leaves, leaf area, diameter of stem, the amount of tuber, length of tuber, diameter of tuber, weight of tuber, yield of tuber, starch and HCN content. The results showed that harvesting age of 6 months had been harvested with the same yield of 9 months harvesting age of 4.33 tons / ha, but the quality of the 9-month harvest age yielded the highest yield with starch content of 44.47% and HCN content of 19.71 ppm.