Vacuum Membrane Distillation (VMD) is one of the membrane distillation (MD) categories which is a technology that depends on creating a pressure difference between the two sides of a membrane using vacuum pressure on the outlet side of the membrane module. A lab-scale VMD system was constructed and operated to study the effect of temperature and salt concentration on salt rejection and permeate flux of the VMD unit with constant feed flow rate and vacuum pressure. The used membrane was a hydrophobic polyethersulfone flat sheet membrane: effective diameter 0.25 m, effective area 0.049 m², pore size 0.2-0.4 µm and membrane thickness 120-160 µm. Permeate flux and salt rejection were measured. Results showed an increase in permeate flux from 15kg/m².h to 25 kg/m².h and in salt rejection from 74% to 80%with the increase in feed water temperature from 40°C to 70°C at salt concentration 5000 ppm ,flow rate 1L/m and vacuum pressure 0.4 bar and the decrease in permeate flux from 15 kg/m².h to 6 kg/m².h and in salt rejection from 74% to 67% with the increase in feed water salt concentration from 5000 ppm to 30000 ppm at temperature 40°C with the same flow rate and vacuum pressure.