Mn-oxide was characterized using X-ray diffractometry, scanning electron, transmission electron microscopy, and thermogravemetric and differential thermal analysis. The surface charge density and zero point if charge (pHzpc) of the solid surface were determined by potentiometic titration. Mn-oxide was subjected to different phosphate concentrations in the pH range 3 to 7 at 303K to investigate the effect of phosphate complexation on the surface properties of solid. The surface compositions before and after phosphate sorption were studied with X-ray photoelectron spectroscopy. The O/OH groups at the surface of Mn-oxide differed with acidity and below pH 6, a drastic change was observed in the O1s peaks in X-ray photoelectron spectrum, due to the dissolution of Mn-oxide. The surface charges arise as a result of H/OH bond breaking and phosphate anions complexation with solid surface. These charges are compensated by counter ions (K+ and NO3-) of the background electrolyte at solid-liquid interface. The phosphate sorption increased with increased phosphate concentration but decreased with pH increasing of the aqueous solution, a process which is the characteristics of metal oxides surfaces. Thus, it was concluded from the present investigation that phosphate anion sorption on Mn oxide have greatly affected the overall surface characteristics of the solid.