A membrane distillation process with brine circulated in the cold side was developed. This process combines the ordinary membrane distillation (MD) with the osmotic distillation (OD), and is therefore called membrane osmotic distillation (MOD). Comparisons of MOD with MD and OD were carried out. It was found that MOD has the advantage of achieving higher water flux and heat efficiency simultaneously. A relation of the MOD water flux to the MID and OD water fluxes was given. In the scope of this work, the water flux arising from a 5 degreesC inlet temperature difference is about 1.5-2.5 times as great as the water flux arising from 1 mol/kg brine concentration. A mathematical model for the MOD process was established and solved numerically. The calculated water fluxes are in good agreement with the experimental water fluxes.