Abstract: Field experiment was conducted to investigate the effect of application paclobutrazol (PBZ) at different growth stages and concentration rates on growth, yield and starch quality of cassava grown under rainfed conditions. The PBZ application reduced plants height and leaf area index, but tend to increased total top dry weight, tuber fresh weight per plant and tuber yield of cassava as compared to untreated control. The tuber yield increased by 12, 35 and 67% over control of application PBZ at concentration rates 10, 20 and 30 ppm, respectively. Paclobutrazol applied at concentration 10, 20 and 30 ppm did not exhibit significantly different on the starch content in tuber as compared to control. Regardless of application at different growth stage, PBZ applied to plants at 210 DAP produced higher tuber yield and starch quality than those of application at 90 and 150 DAP.