The study on the drainage has been performed for long time in Korea. The 4th attempt of study on under-drainage by use P.V.C. suction pipe were made in 1971. Drainage method, soil temperature, growth of crop and yield were observed and compared with the 3 drained Plots and at the 3 undrained ones. Obtained results were as follows; 1. The soil temperatures in the drained plots were 1.8℃ higher than that in the undrained ones during the irrigation period. 2. 20% of increased yield were resulted from practicing of P.V.C. suction pipe drainage. 3. The annual net income per 1ha of paddy rice field with P.V.C. suction pipe drainge was 82,900 won.