The losses of tropical peat swamp forests have triggered serious environmental problems such as emission of greenhouse gases and loss of biodiversity. The amount of carbon emissions as a result of fires in peatlands are particularly high, as peat is extremely rich in belowground organic carbon. To prevent peat fire, high watertable has been unconditionally assumed to be important. However not only high water table but also continuous capillary of peat soil is important as it control peat moisture above watertable. If peat capillary is discontinuous surface peat would dry even under high watertable condition and easy to burn. It means high vulnerability to fire and high rate of oxidation. Eventually such peat is not sustainable. In the present study, we evaluate peat vulnerability to fire by measuring moisture retention and thermogravimetric curve of both tropical and boreal peat.