Recently, mass screening for gastric cancer has been popularized in Japan. In the screening, gastric radiography is carried out using a contrast medium, usually barium sulfate. Recently, a high concentration barium sulfate has been developed and is currently used in several medical facilities. However, high concentration barium sulfate flows out of the stomach faster than a solution of lower concentration used in the past, which interferes with the diagnosis. The flow rate is dependent on the viscosity of barium sulfate, which changes based on gastric pH and temperature. In this study, the viscosity changes of barium sulfate induced by pH and temperature changes were examined. Two types of high concentration barium sulfate, 185B barium and 200C barium, and one type of moderate concentration barium sulfate, 145A barium, were used in this study. The radiographs of gastric phantoms applied with the three types of barium sulfate were also tested under several different pH and temperature conditions. Furthermore, we analyzed the particle size distribution of the three types of barium sulfate. The results indicated that 185B barium is the best among three types tested for gastric radiography. This study of characteristics of barium sulfate may improve radiography technology in mass screenings for gastric cancer.