In this study, variation of contrast-noise ratio and mean glanduler dose have been evaluated for increasing breast thickness in mammographic application. Measurements were carried out in the Siemens Mammomat Inspiration full-field digital mammography unit by using polymethyl-methacrylate phantom (PMMA) in order to simulate different breast thicknesses. Contrast-to-Noise Ratio (CNR) and Mean Glanduler Dose Value (MGD) were calculated for each PMMA thickness which starting from 20mm to 60mm in Automatic Exposure Control (AEC) mode according to the method provided by European Guidelines and the results were compared to acceptable values. It was determined that MGD values gradually increase and CNR values decrease with increasing breast thickness. For each breast thickness CNR and MGD values were determined in the acceptaple limits which are suggested by the European Guidelines.