Bamboo invasion is known to affect soil properties; however, its impact on soil solution chemistry remains poorly understood. This study investigated how bamboo invasion affects major ion concentrations, their vertical distribution, and the distinct ionic compositions maintaining charge balance in soil solution by comparing Moso bamboo (BF) and adjacent Japanese cedar (CF) forests. In the surface soil solution (5 cm) , most ions were significantly higher in CF than in BF, possibly due to the accelerated rock weathering and greater NO₃⁻ accumulation resulting from lower N uptake in CF. Regarding vertical distribution patterns, in CF, almost all ion concentrations were significantly higher in the surface soil solution than in the soil leachate (50 cm), whereas in BF, this phenomenon was observed solely for NO₃⁻, NH₄⁺, and K⁺, likely due to bamboo's high demand for these primary macronutrients. A significant correlation between NO₃⁻ and Ca²⁺/Mg²⁺ concentrations was absent only in the soil leachate of BF. Conversely, anion deficit showed a significant correlation with Ca²⁺/Mg²⁺ in BF soil leachate, with HCO₃⁻ identified as a major component of this deficit. Our study indicates that bamboo invasion could alter soil solution chemistry, leading to impacts on forest soil nutrient availability and downstream water quality.