The liquid phase plasma reduction method was applied to prepare the polycrystalline manganese nanoparticles from the solution of manganese chloride tetrahydrate. A bipolar pulsed power supply was used to generate discharge in the aqueous solutions. While large size of dendrite-shaped manganese nanoparticles were mostly observed in the initial stage and particle size decreased with discharge time. The particles were dispersed with less and less small particles by the addition of CTAB and anisotropic shapes nanoparticles were mostly observed at long time plasma-treated. Many spots could be seen in the ED pattern for polycrystalline particles.