The experimental and theoretical study of a solar desalination system located in Cairo, Egypt, is presented in this research. A modification unit is provided to enhance the performance of the solar desalination. The modification unit includes a solar parabolic trough (solar energy concentrator) with focal pipe and simple heat exchanger (serpentine) Oil is selected as working fluid. Oil is flowing as cycle through the focal pipe and serpentine. Oil has high thermal properties. The modification unit is utilized during sun duration and night. The oil in the heat exchanger is heated during the sunlight by two purposes, direct solar radiation and solar energy concentrator (solar parabolic trough). The parabolic trough is tracking the sun using simple mechanism to collect the highest amount of solar radiation by optimum angle. The trough is covered with transparent plastic sheet to avoid the heat transfer by convection to the surrounding (i.e. the green house effect is utilized). Copper serpentine of the heat exchanger is painted by Black color and is installed in the bottom of the still basin. It is attached extremely with thermally insulated pipelines through the trough. The oil is forced flow using small pump which may be powered by PV system. The saline water is heated directly by solar radiation and also, by the oil in the heat exchanger as the oil cycle. The thermal analysis of the proposed solar desalination system is expressed using the energy balance equations for different components of the system. The performance curve of the pump and the characteristics of the motor are illustrated. The overall efficiency of the proposed system is computed. Two experiments are carried out at April and June 2005. Type-K thermocouples (+/- 0.5 degrees C), digital temperature devise and remote control unit are used for measuring the system temperature points. The forecast of the typical climatic conditions of the experimental Cairo site at the selected days are obtained from the "Egyptian Solar Radiation Atlas" of the Geophysical Institute. The comparison between the performance of the conventional and the modified solar desalination systems is presented. The economic study of the present system is determined. The results show that fresh water productivity is increased by an average of 18%, due to the modification.