An experimental study has been carried Put to compare the performance of natural and forced circulation domestic solar water heaters. Several measurments have been made for the two cases which included; the collector water inlet and outlet temperatures, the mass flow rate, the tank temperature, the ambient temperature and the solar insolation, The main parameters for the solar collector are calculated for the natural and forced circulation systems, These included; the top, back, and overall loss coefficients, the heat removal factor, the efficiency factor, the useful energy gain and the instantaneous efficiency, The comparison showed that the efficiency of the forced circulation system could be 35 to 80% higher,