Manganese dioxide (MnO₂) has recently attracted significant attention as a cathode material for zinc-ion batteries (ZIBs) due to its outstanding advantages, including environmental friendliness, non-toxicity, and high specific capacity. However, commercially available MnO₂ typically exhibits large and irregular particle sizes, which adversely affect its electrochemical performance. In this study, MnO₂ was synthesized from manganese precursors, including MnCl₂, Mn(CH₃COO)₂, and MnSO₄, via a hydrothermal method to optimize the synthesis process and obtain MnO₂ with uniform, nanoscale particle size suitable for aqueous pouch-type Zn-ion batteries. Among the synthesized materials, MnO₂ derived from MnCl₂ exhibited superior electrochemical properties, achieving a charge/discharge efficiency of over 95% and a high specific capacity of approximately 200 mAh/g at a current rate of 0.6C.