A thorax is consisted of a heart, great vesseles, lungs, ribs, sternum and thoracic spine etc. The quality of chest radiogram is very important in order to find out abnormality in the lung field. The image has two major characteristics; density and contrast which directly influence the diagnostic quality of the roentgenogram. It is very hard to make excellent film image in the lung field because of overlapping bones and other soft tissues. To take a good radiogram of lung field, we studied the condition of chest P-A projection in adult and obtained results as follows: 1. The average chest radiographic condition is resulted as 62KVP, 16 mAs in hospitals around Kyung Ki-Do, Korea, 2. The density of the chest 20cm in thickness, is equal to the water phantom 8cm in thickness. 3. The best quality of chest radiogram is achieved in the condition of the lung field at 100KVP, 9.6mAs by use of Grid 8:1.