AbstractMagnesium oxalate dihydrate was used as a “generator” to produce active magnesium oxide by heating bothin vacuoand in presence of constant water vapour pressure. Results indicate that sintering is accelerated in presence of water vapour and probably takes place by a different mechanism than by heatingin vacuo.Sinteringin vacuois accompanied by widening of pores, whereas in presence of water vapour it is accompanied by narrowing of pores. The role played by water vapour in accelerating the sintering of magnesia is discussed and possible explanations are offered. Dual effects of water vapour might lead to the sintering acceleration of magnesia; chemisorption of OH groups which create cation vacancy on the surface leading to activated surface diffusion, and oxygen bridging between two adjacent/or opposite OH groups, particularly in narrow pores, leading to their narrow