The experiment was carried out in the Upland Crops Research Area - Thai Nguyen University of Agriculture and Forestry - with 5 harvesting time (5 treatments, treatment No.1 was harvested on 15th of November, the following treatments were 20 days later). The experiment was arranged in a complete randomized block design with three replications. Experimental results showed that achira plants in studied treatments had the same plant height, stem diameter, number of leaves/main stem and homogeneity. Treatment No.3 and 4 (harvested after 10 months and 10 months 20 days of growing, respectively) had fresh tuber yield, dry matter yield and the highest starch yield (yield ranged from 75.36 to 76.18 tonslha
dry matter yield reached 18.97 to 20.14 tons/ha and starch yield reached 10.47 to 11.2 tonslha). Achira plants growing in Thai Nguyen can be harvested since 9 months after planting, however, the best time to harvest after planting is from 10 months to 10 months 20 days. Harvesting before 9 months of growing can reduce both fresh tuber yield, dry matter ,yield and starch yield. Harvesting after more than 11 months of growing had no significantly affects on.fresh tuber yield but remarkerbaly reduced the dry matter yield and starch yield.