Background: This study aims to evaluate the effect of ultrasonography (US) on quality of cardiopulmonary resuscitation (CPR), and US-related pause duration of pulse-checks.Methods: This retrospective observational study was conducted at the emergency department of National Taiwan University Hospital between April 2017 and May 2018. Video recordings for adult patients with non-traumatic cardiac arrest in designated resuscitation rooms were collected. The primary outcome was chest compression fraction (CCF) in the CPR with US group. The secondary outcome was pause duration of pulse checks with introduction of US or not. US-related pulse-checks were stratified into US during hands-off periods only (hands-off US), and US performing from hands-off to hands-on periods (continuous US). Results: A total of 153 patients were enrolled. Continuous US was performed in 116 patients. CCF was similar (92%) between the CPR with and without US groups. In the CPR with US group, pause duration was significantly longer in US-related pulse-checks than that without US (9.3±8.0 v.s. 7.3±4.7s, p<0.0001). Notably, longer pause was noted in the hands-off US, as comparing with that in the continuous US (18.3±16.4 v.s. 7.7±3.5s, p<0.0001). Conclusions: The introduction of US during CPR did not impact on CCF. Individual pause would not be lengthened if continuous US was performed while allowing chest compressions to be resumed. In addition, structured training, adequate facilities and manpower, and a timer reminding resumption of chest compressions would help sophisticated integration of US into CPR process.