A small domestic solar water heating system in thermosyphonic flow was tested in Seoul. The system consisted of four flat plate aluminium roll bond type collectors of total effective area $3.28m^2$ and a $280{iota}$ storage tank. It was tilted $52^{circ}$ relative to the horizon. And the collector plate, collector tube and storage tank were equiped with 14 thermocouples. As the results, the following facts were found; 1) To provide water at $55^{circ}C$ for a family of four in Seoul, a collector area of $3-4m^2$ and a storage capacity of $180{iota}- 200{iota}$ are suggested. And this system can supply hot water at above $45^{circ}C$ day about. 2) In the late afternoon hours, it might be advantageous to stop the flow in the system as heat losses to the environment increase unduly. 3) Without any hot water consumption throughout the day, water temperature distributions inside the storage tank was found almost linear. This indicates essentially no mixing inside the storage tank. 4) In case of a small domestic solar water heating system, it is better to employ a single transparent cover rather than double one.