Manganese oxides having birnessite structure have been successfully synthesized by precipitation method. These materials were fabricated based on the reaction between KMnO4 and citric acid or oxalic acid as reductant. The precipitated solid products were heated up to 120 °C and calcined up to 600 °C. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), and its average oxidation state (AOS) together with the zero point charge (pHzpc) were also determined. The XRD results showed the calcined citric-prepared birnessite displayed more crystalline structure than oxalic-prepared birnessite. The SEM results indicated that the citric precursor produced aggregation particles with needle-like appearance on its crystal faces, while oxalic acid generated irregular aggregation particles. The catalytic activities of as-prepared birnessite prior to and following to calcinations were evaluated for the degradation of methylene blue (MB) with H2O2 as an oxidant. The un-calcined samples displayed much higher catalytic degradation for MB compared to calcined samples. The maximum of MB degradation obtained using un-calcined catalyst from citric acid precursor was 98%, whereas the oxalic acid was 90%. The high catalytic activity of un-calcined samples especially for citric-prepared birnessite was correlated with high defect concentration due to its low AOS Mn and small crystal size.