Variety SC205 widely cultivated across South China was used as test material, a field experiment with three K₂ O rates, i.e. 0 (CK), 120 and 240 kg/hm² was conducted to investigate the effects of potassium fertilization on the growth, potassium contents and accumulations, potassium use efficiency of cassava. Dry matter and K contents of leaves, stems, fibrous roots and storage roots were measured in diffident growth stages of cassava, meanwhile, agronomic characters and fresh root yield (FRY) were measured at harvest stage of cassava. The results showed that, 1) compared with CK, K fertilization significantly improved the plant height, leaf area, leaf area index, chlorophyll content and FRY of cassava by 16.1%-19.0%, 3.8%-8.4%, 12.8%-18.2%, 13.6%-17.3%, 12.8%-29.4% and 9.9%-25.6%, respectively. FRY of K₂ O 120 kg/hm² was the highest (27.1 t/hm²). 2) K fertilization extremely significantly increased K contents and uptakes, but no significant difference in K uptakes of different organs between the treatments of K₂ O 120 kg/hm² and 240 kg/hm². K contents in various organs were an order of leaf > stem > fibrous root > storage root. With the growth of cassava, the main K uptake organ of cassava shifted from leaf to stem and fibrous root. 3) With the increment of K fertilization rate, K use efficiency, K physiology efficiency, K utilization efficiency and K harvest index of cassava decreased significantly while K absorption per 100 kg fresh storage root increased significantly. Based on FRY, K accumulation and K use efficiency, 120 kg/hm² of K₂ O fertilization is optimal for cassava.