Abstract: Objective: To compare the image quality between two CT scanners under two different tube voltages using a dedicated phantom. Materials and Methods: Siemens SOMATOM Force CT and Phillips Spectral IQon CT were used for scanning and the dedicated Assurance Quality Phantom Catphan 500 was applied. Module CTP 528 and CTP 515 were performed for evaluation of high resolution and low-contrast sensitivity, respectively. Four sets of images of two scanners were acquired, including group A to D whic represented force 120 kVp, force 140 kVp, IQon 120 kVp and IQon 140 kVp. The dosage of all four set of images was 20mGy.Evaluation of high resolution was carried out by two radiologists via the smallest line pair one could distinguish and low-contrast sensitivity was measured by the smallest diameter under 1% contrast. Mean noise, signal-to -oise ratio (SNR) and contrast-to-noise ratio (CNR) were also evaluated for each group. Results: Group A and C had the highest high resolution with a line pair of 6 lp/cm; the same low-contrast sensitivity was observed by all the groups (diameter of 5 mm). Group A showed the smallest noise (2.500±0.000) and highest SNR (30.806±1.398). Noise and SNR were both significantly different among four groups. The highest CNR (3.325±0.300) was observed in Group D, but no statistical difference was found among the four groups. Conclusion: Image quality varied under different CT scanners and tube voltages. Images with 120 kVp showed better contrast compared with those with 140 kVp. 120 kVp with force CT showed improved image noise than that of 140 kVp images; while for IQon spectral CT, no obvious difference in noise parameters was found between the two tube voltages.