Objective: The purpose of the study was to evaluate the qualitative and semi- quantitative effects of using different low- dose computed tomography (CT) matrix sizes for attenuation correction of PET images. Methods: Co-registered 2-[F18]- fluoro-2-deoxy-D-glucose (FDG)-PET and CT images were acquired using a combined PET/CT scanner according to a standardized protocol. PET/CT reconstruction was repeated using default reconstruction protocols with different matrix sizes for low dose CT (512,768 and 1024) in 25 patients. The resulting images were analyzed qualitatively “image quality” and semi-quantitatively using “mean SUV & Signal to Noise Ratio (SNR)”. Results: No significant difference in the resulting attenuated corrected images reconstructed with the different matrix sizes either qualitatively or semi- quantitatively. Conclusion: The matrix size of the low dose CT used in the attenuation correction of PET images does not affect the image quality or semi-quantitative parameters.