Abstract: Diagnostic Digital Radiography (DR) systems may result in an excessive exposure of radiation, since, there are no limitations about exposure levels to acquire the required medical images. This study aimed to understand the proper dose of diagnostic DR equipment and to investigate SI when DICOM image was captured and exposure level when it was tested according to automatic exposure control and manual modes. Four diagnostic DR systems and a chest phantom were used. DICOM images were captured in the chest PA test and their exposure levels were 5 times measured using a dosimeter, establishing AEC and manual modes, respectively, during the chest PA test. The SI for captured DICOM images was recorded by establishing an ROI with image J. The statistical analysis was performed utilizing the Mann-Whitney test. Measurements of the diagnostic DR system yielded SI values that differed by manufacturers and ROIs of DICOM images while AEC and manual modes of the same manufacturer’s equipment did not. The exposure level in the AEC mode compared to the manual mode was measured to be lower by 5.7% in S company’s equipment by 49% for the P company by 2.1% for the G company and by 187.2% for the C company one. The differences among the four DR systems was statistically significant (p<0.05). It is suggested to use radiographic tests of outstanding image quality flexibly with lower doses in consideration of the equipment characteristics and patient’s physical conditions, recognizing that excellent medical images can be captured with lower doses in the DR system by the manual mode than by AEC. Since, the AEC function in the diagnostic DR system may not capture the medical image at lowest exposure levels, manual modes that take patient’s physical conditions into account are thought to contribute in the reduction of doses.