The compound beryllium oxalate trihydrate decomposes on heat treatment to beryllium oxide. Preparation of samples of beryllium oxalate under varying conditions revealed that the oxalate is hygroscopic and can exist as a trihydrate, a monohydrate or a combination of both depending on the partial pressure of water Vapor above the sample. The dehydration of these samples was shown by the thermogravimetric data to be followed by a subsequent one-step decomposition to BeO. There was some indication of intermediate compounds existing in the decomposition to the BeO. The kinetic behavior of this latter stage was studied in a series of isothermal experiments and was best described by a D2 diffusion mechanism with an activation energy of 88.9 kJ mol(-1). This is lower than that commonly reported for other Group II oxalates which suggests a less stable oxalate. By decomposing the beryllium oxalates at various temperatures, the surface area of the solid residue increases with a loss of crystal morphology but the oxide product resists sintering.