1. Title of Research Research on the Loss of Irrigation Water Flowing in Earth Channel. 2. Purpose and Importance of Research The purpose of this research is to obtain the accurate loss rated of irrigation water flowing in earth channels so as to give a criterion of designing rational and effective suplpy project of irrigations water. It is the present status that the loss rates of 10 to 20% are obscurely applied without any scientific proof. Therefore, the importance of this research lies in securing loss rates, which are experimentally proves to be suitable for specific local conditions. 3. Content and Scope of Research The selected test reach of the main channel is 1,000m long. Discharges were measured at up and downstream enps by using current meter. The test reach of the lateral channel is 500m long, and parshall flumes were set at both ends to measure inflow and outflow. Finally, for the supply ditch, the test section is 200m long, and sharp-edged rectangular weirs were provided at both ends to measure inflow and outflow. In addition, various factors influence on the loss of irrigation water in channel wer examined. 4. Results of Research and Proposition Results: 1. In the main channel, which is 1,000 M long, and has a slope of 1/3,000 and was constructed by cutting earth, its loss rate is 9.64%. 2. In the lateral, which has a slope of 1/1,500, and is 500m long, and was constructed by cutting, its loss rate is 15.55%. Its average seepage rate is 2.08cm/day. 3. In the supply ditch, which has a slope of 1/300, and is 200m long, and was constructed by filling earth, its loss rate is 12.34%, its average seepage rate being 3.37cm/day. Proposition: As could be seen in the results above-mentioned, it is contradictory to apply a loss rate of 20% for every main channels and 15% for every laterals without variation, as done so for in planning irrigation project. The fact, however, is that loss rates must be different according to localities and characteristics. Due to the fact that this experiment is small in its scope and is nothing but a preliminary one, it is hardly possible to draw decisive conclusions with the results obtained in this research. Loss rates, that are secured through more extensive research, should be used, in order to establish precise irrigation project. Moreover, such researches should be carried out for a number of loclities throughout the nation.