Biochar has been widely suggested as an effective amendment to improve crop growth and productivity. However, its long-term effects on rice growth and productivity, especially in acidic paddy are less understood. We conducted a five-year (2015-2019) field experiment with the single factor randomized block design in an acidic paddy of Changsha, Hunan Province, south China. We aim to investigate (1) how do rice growth and productivity respond to different amount of biochar amendment (i.e., 0 t/hm² (CK), 20 t/hm² (B20), 40 t/hm² (B40), 60 t/hm² (B60), 80 t/hm² (B80), and 100 t/hm² (B100))? and (2) how long can the effects of biochar amendment sustain? The results showed that: (1) leaf area index (LAI), the chlorophyll content of the reciprocal fourth leaf, and dry matter accumulation at the heading stage increased with the increasing amount of biochar amendment, so did the rice yield. (2) Biochar amendment showed no significant effects on the chlorophyll content of the flag leaf at the heading stage and the grain-leaf area ratio. (3) The amount of biochar amendment significantly impacted its role in increasing rice yield. Rice yield significantly increased 17.0%-23.7% in the first year with ≥ 60 t/hm² biochar amendment compared with CK). The corresponding numbers for the other four years were 15.5%-32.4% rice yield increase with ≥40 t/hm² biochar amendment in the second year, 9.6%-21.8% rice yield increase with 20-100 t/hm² biochar amendment in the third year, no significant increase for all treatments in the fourth year, and 15.7% rice yield increase with 100 t/hm² biochar amendment in the fifth year. (4) Biochar amendment increased the accumulated rice yield for the consecutive five years by 9%-23.7%, 5.5%-27.8%, 6.8%-25.9%, 5.4%-22.0%, and 4.6%-20.6%, respectively. (5) Rice yield significantly correlated with LAI, the chlorophyll content of the reciprocal fourth leaf, and dry matter accumulation at the heading stage, and also significantly correlated with grain number per panicle. We found that biochar amendment could significantly improve rice growth and productivity in acidic paddy and the effects were stronger with higher amount of biochar amendment (i.e., 80 t/hm² and 100 t/hm²). We also found these effects could sustain at least three years. The findings of this study can extend our understanding of the long-term effects of biochar amendment on rice growth and productivity and can also help farmers to increase rice yield through proper biochar amendment in acidic paddy.