the hydrophobic cellulose nitrate microporous composite membranes have been obtained by modification of hydrophilic cellulose nitrate microporous membranes by the use of plasma polymerization of octafluorocyclobutane. The obtained hydrophobic microporous composite membranes have been used in membrane distillation (MD) process. The effect of preparation condition of the membranes on their structure and performance has been investigated by SEM