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Introduction: The effect of on-scene number and level of emergency medical technicians (EMTs) on the outcome of patients with out-of-hospital cardiac arrest (OHCA) remains unclear. In Taipei city, the respond number of EMTs for an OHCA ranged from 2 to 6 and the levels included EMT-intermediate (EMT-I) and EMT-paramedic (EMT-P). Hypothesis: We tested the hypothesis that for adult, non-trauma OHCA patient, on-scene EMT number more than 2 or level of the EMT-P ratio >50%, comparing to crews with two EMT-Is, would improve survival to hospital discharge. Methods: We analyzed five years of Utstein-based registry data on OHCA in Taipei. The eligible patients were non-traumatic adult OHCA with resuscitation attempts. The exposures were the total number of EMT or the EMT-P ratio >50%. The outcome was survival to discharge. Subgroup analyses were based on Utstein template. Results: From 2011 to 2015, there were 8,262 cases included. The average of on-scene EMT number was 3.0 ± 1.0, and a total of 1085 (13.1%) OHCAs was approached by crews of EMT-P ratio >50%. The overall cases of survival to discharge were 616 (7.5%). While the increase of one EMT on-scene was not associated with better chances of survival (adjusted odds ratio [aOR] 0.98; 95% confidence interval [CI]: 0.89-1.08), the level with the EMT-P ratio >50% was associated with improved outcome (aOR 1.36; 95%CI: 1.06-1.76). Subgroup analyses showed that EMT-P >50% significantly benefited the outcome in witnessed OHCAs with non-shockable rhythm (aOR 1.69; 95%CI: 1.01-2.58). Taking both number and level into consideration (figure) , the best survival to discharge occurred at 4 EMTs with the EMT-P ratio >50% (aOR 2.54; 95%CI: 1.43-4.50) when compared to crews with two EMTs. Conclusions: On-scene EMT-P ratio >50% was associated with improved survival to discharge of OHCAs, especially in those with witnessed, non-shockable rhythm. The presence of four EMTs with EMTP-ratio >50% at the scene of OHCA was associated with the best outcome.