The dehydration of (NH4)2C2O4 . H2O has been studied by isothermal and non-isothermal TG. From the non-isothermal experiments, the best-fitting rate law appears to be Al.5, A3, or D3. Data from isothermal experiments gave the best fit with an R2 rate law. A value of 73 kJ mol-1 was found for the activation energy, and the nature of the variation between runs was explored.