|Purpose: The quality of cardiopulmonary resuscitation (CPR) has been identified as an important factor for improving survival rate. This prospective study was conducted for comparison of manual chest compression and mechanical chest compression during simulative out of hospital cardiac arrest. And evaluation of quality of manual compression was performed on-scene and during ambulance transportation. Methods: A total of 24 emergency medical technicians (EMTs) participated in our study. During a period of one month, they were educated by E-learning on the importance of decreasing hands off time during CPR and anything else about CPR. We instituted the scenario of out of hospital cardiac arrest. They performed CPR twice in each same situation: they performed manual chest compression the first time. And, the second time, they used the mechanical chest compression device (X-CPRTM). We evaluated the performance by camcorder monitoring and Q-CPRTM for measurement of manual compression depth and flow time. Results: A total of 48 cases were performed in this study. Twenty four cases were included in the manual CPR group (H-Group) and 24 cases were included in the mechanical group (M-group). CPR of the H group vs. the M group was performed for a mean 19.71±2.97 min, 21.95±4.16 min on scene, and in a moving ambulance. The average compression rate was 122±14.80 min-1 vs 104.38±6.40 min-1 (p<0.001), and the compression depth was 44.25±8.50 mm vs 42.37±4.28 mm (p=0.34), respectively. No statistical difference was observed in the flow time ratio between manual and mechanical chest compression (67.04±11.12 vs 64.13±6.61, p=0.28). However, the quality of compression of the H-group, the ratio of insufficient compression, and the ratio of insufficient release during transport were higher than those on-scene (p=0.02, p=0.01). Conclusion: In comparison of chest compression rates between the two groups, the M-group showed a higher rate of chest compression. However, no significant difference in chest compression depth and flow time ratio was observed between the H- and M-groups. When performing manual chest compression during transport, EMTs should be careful of adequate chest compression and release.