Phytolacca acinosa Roxb. is a Mn hyperaccumulating plant. In the present study, the chemical forms of Mn in the leaves of P. acinosa were investigated using chemical analyses and X-ray absorption spectroscopy (XAS). P. acinosa plants were grown hydroponically with 2 mM Mn for 28 days. About 80% of the Mn in the leaves of P. acinosa was found in the supernatant fraction after centrifugation at 20,000g for 45 min. The supernatant fraction was then used to identify the chemical forms of Mn. Gel filtration analysis (Sephadex G-10) showed that oxalate and Mn appeared in the same fraction of the supernatant and the molar ratio of oxalic acid to Mn was 1.12, indicating that there was sufficient oxalic acid in P. acinosa leaves to complex Mn. XAS was employed to investigate the chemical species of Mn in leaves of P. acinosa. Results showed that Mn in leaves was bivalent and almost 90% of the total Mn was Mn-oxalate. The oxalate concentration in the leaves of P. acinosa was not affected by increasing Mn concentration in the solution, suggesting that oxalate biosynthesis was not induced by Mn.