Background and Aim：The purpose of this study was to observe the changes over time in liver stiffness measured by shear wave elastography（SWE）in hepatitis C patients during direct-acting antiviral agent（DAA）treatment and evaluate the factors affecting the liver stiffness.Methods：The subjects were 206 consecutive patients diagnosed with hepatitis C in the Dokkyo Medical University Saitama Medical Center treated with DAAs. SWE was performed to measure the propagation velocity of shear waves（Vs）before starting treatment（baseline）, at the end of treatment（EOT）, and 12 weeks after EOT（follow-up 12）. The change in Vs（ΔVs）was calculated for the difference between baseline and follow-up 12. Clinical parameters were obtained on the same day as SWE. Multiple regression analysis was used to identify factors related to ΔVs.Results：Data from 149 patients were used；all 149 patients achieved sustained virological response. Mean Vs decreased significantly, from 1.58±0.92 m/s at baseline to 1.46±0.27 m/s at EOT（P＝0.00045）. Mean Vs at follow-up 12 was 1.42±0.28 m/s, significantly lower than at EOT（P＝0.00002）. The mean ΔVs was 0.147±0.164 m/s. On multiple regression analysis, prothrombin time％（PT％）and the change in alanine aminotransferase（ΔALT）from baseline were significantly related to ΔVs. Baseline ALT and the FIB4-index tended to affect ΔVs.Conclusions：In hepatitis C patients, Vs measured by SWE improved with 12 weeks of DAA therapyand continued to improve to follow-up 12. Baseline PT％ and ΔALT contributed significantly to theimprovement of Vs during DAA treatment, and the FIB-4 index also had a great effect
