Manganese mineral phases in polymetallic nodules from Pacific Basin have been studied by means of TEM, XRD and FTIR. Six mineral phases viz. vernadite, todorokite, birnessite,buserite, buserite- asbolite mixed-layer mineral and woodruffite, have been identified. Their morphological and microstructural features have been described. In Central Pacific Ocean, nodules in CP zone are rich in vernadite and,next, todorokite,whereas in CC zone the sheet todorokite is dominant and vernadite comes second. Xodules from Fast Pacific basin are rich in lamellar todorokite and buserite, with minor vernadite. The IR spectroscopic study shows that condensed octahedral unite of MnO6 exist in the structure of vernadite, todorokite, birnessite,but the strength of Mn一O bond decreases gradually in order of todorokite, birnessite, vernadite. Relationships of the phase transformation among manganese minerals were inquired into.Phenomena of phase transformation between vernadite and todorokite and between layered buserite and vernadite were discovered .The result of heat treatment shows that up to 105 C buserite-I may be transformed into birnessite owing to dewatering, and there is no phase trans- formation between todorokite and birnessite; up to 400℃ layered buserite may be transformed into vernadite, but there exists no structural change for fibrous todorokite with tunnel structure.