Introduction: This work aimed to determine local diagnostic reference levels (local DRLs) for screening mammography at Songklanagarind Hospital on digital mammography. Materials and methods: Retrospective data of screening mammography were collected from 400 patients from Songklanagarind Hospital, 200 patients from Tanyawej Breast Center and 200 patients from Premium Diagnostic Imaging Center. The patients were women aged between 40-75 years old with compressed breast thickness between 41-65 mm. and undertaken screening mammogram during 1st January 2019 – 31st October 2020. Patient data and exposure parameters collected were as follows: average glandular dose (AGD), entrance surface air kerma (ESAK), compressed breast thickness (CBT), compression force (CF), peak kilovoltage (kVp), tube current-time (mAs), target and filter (W/Rh, W/Al), and patient age. Results: The result showed that the average glandular dose of FFDM (2D mode) and DBT (3D mode) for compressed breast thickness 41-65 mm were 1.41±0.43 and 1.68±0.39 mGy, respectively and the 75th percentile of FFDM (2D mode) and DBT (3D mode) were 1.65 mGy and 1.89 mGy, respectively. The average ESAK were 4.93±1.96 mGy in FFDM (2D mode) and 5.31±1.55 mGy in DBT (3D mode), respectively. The 75th percentile of ESAK in FFDM (2D mode) and DBT (3D mode) were 6.03 and 6.17 mGy, respectively. There were 24.88 % and 24.63% received the average glandular dose over the 75th percentile in FFDM (2D mode) and DBT (3D mode). Conclusion: Local Diagnostic Reference Levels for FFDM (2D mode) and DBT (3D mode) at Songklanagarind Hospital were 1.65 mGy and 1.89 mGy. The Local DRLs in our study was safe and lower than the standard reference levels reported by the International Atomic Energy Agency at 3 mGy/view.