Introduction: The efficacy of epinephrine (Ep) administration to cardiopulmonary arrest (CPA) patients is still controversial, and correlation between plasma Ep levels of and prognosis in CPA patients is unclear. Hypothesis: We hypothesized that the more EP is administered, the higher the rate of ROSC becomes in CPA patients. The purpose of this study is to evaluate whether a dose of Ep influenced the prognosis in CPA patients. Methods: This was a prospective, observational clinical study, approved by the ethics committee of Gunma University Hospital (IRB #14-13). CPA patients transferred to our hospital were enrolled prospectively between July 2014 and July 2017. The levels of Ep in the plasma were measured using blood samples immediately obtained at the time of arrival to our hospital. Patients were divided into the four groups based on the prehospital administered dose of EP; patients without prehospital Ep administration (group Z), prehospital administration of 1mg Ep (group O), 2mg Ep (group T) and 4mg Ep (group F). The plasma Ep levels and the conditions of resuscitation were compared among those groups. The IBM SPSS Statistics 25 software was used for statistical analysis. Data are shown as median (Q1, Q3). The Kruskal-Wallis or chi-square tests were used to conduct the comparisons among four groups. P<0.05 denoted statistical significance. Results: We analyzed 150 patients. There were 96 patients in group Z, 38 in group O, 11 in group T and 5 in group F. There was no significant difference in prehospital resuscitation time among 4 groups, and the level of Ep in the plasma obtained immediately after arrival at hospital was the highest in the group F with a significant difference {286.0 (247.2, 424.9) ng/ml in group F, 244.0 (22.1, 620.3) ng/ml in group T, 1.6 (0.5, 4.5) ng/ml in group O and 2.0 (0.4, 4.5) ng/ml in group Z, respectively, p<0.001}. However, the ratio of ROSC acquisition was the lowest in the group F with a significant difference (0 in group F, 18.2% in group T, 15.8% in group O and 35.4% in group Z). Conclusions: Our results suggest that the prehospital administered dose of Ep is not relates with the acquisition of ROSC in patients with CPA.