Abstract: Abstract: [Objective] Plants grown on acid soils are affected by a number of barriers, among which manganese toxicity is the second important factor limiting plant growth following aluminum toxicity. The purpose of this study was to alleviate the acidification and toxic effect of manganese in acid soil. [Method] We designed an one month laboratory incubation experiment to study the effects of two different biochar: rice-husk-based charcoal and apple-branch-based charcoal with an addition of 3%, respectively, on the growth and manganese accumulation of water spinach on acid soil, as well as the melioration effect under the addition of exogenous manganese (2mmol·kg-1 and 4 mmol·kg-1). [Result] Our results show that: (1) A significant increase of the plant height and biomass of water spinach were tested with the addition of rice-husk-based charcoal and apple-branch-based charcoal; the addition of rice-husk-based charcoal significantly reduced the inhibition of exogenous manganese on the growth of water spinach, while apple-branch-based charcoal did not make a significant effect；two kinds of biochar significantly alleviate the water deficit in spinach caused by the high exogenous manganese toxicity. (2) Biochar addition significantly increased soil pH value which had significant or extremely significant correlation with the height and biomass of water spinach. (3) The manganese content of spinach grown significantly reduced by 48.5% and 26.6% as the addition of rice-husk-based charcoal and apple-branch-based charcoal, respectively; meanwhile, the addition of rice-husk-based charcoal significantly decreased manganese content of spinach to 516.4~975.5mg·kg-1 grown on exogenous manganese added soil, which caused an enrichment of manganese to 1502.1~2185.9mg·kg-1; apple-branch-based charcoal did not effectively alleviate the toxicity of exogenous manganese on water spinach. (4) Biochar, especial the rice-husk-based charcoal, significantly decreased the exchangeable manganese content and increased the labile reduction manganese content in soil, but showed no significant influence on total active manganese content. [Conclusion] The addition of rice-husk-based charcoal and apple-branch-based charcoal significantly increased the growth of water spinach and alleviate the water deficit in spinach caused by exogenous manganese toxicity; Two kinds of biochar significantly alleviated the accumulation of manganese in water spinach, increased soil pH, decreased soil exchangeable manganese content, and, in different degrees, alleviated manganese toxicity and promoted plant growth.