Objective The present study aimed to determine the relationship between the triage-based resource allocation and clinical treatment (TRACT) protocol and mortality and length of stay (LOS) in ED. Methods This before-and-after study was conducted in an adult, tertiary, teaching hospital ED from August 2008 to July 2012. Patients who were younger than 18 years of age, who were dead on arrival and whose triage information was not available were excluded. TRACT was implemented in August 2010, and the Emergency Severity Index (ESI) was used for triage. Primary and secondary outcomes were ED mortality and ED LOS. Multivariate logistic regression models for ED mortality and multivariable general linear models on the ED LOS were used to compare the before- and after-intervention periods. Results For the 155 563 visits over study period, the ED mortality rate was 0.2%, and the ED LOS was 4.6 h (median). The adjusted odds ratios (95% confidence intervals [CIs]) of the TRACT protocol on ED mortality were 0.69 (0.54–0.88) for total patients, 0.42 (0.30–0.59) for ESI 1, 1.04 (0.66–1.65) for ESI 2 and 1.45 (0.76–2.75) for ESI 3 group. The adjusted coefficients (95% CIs) of the TRACT on the ED LOS were −88.1 (−96.9 ∼ −79.2) min for all patients, −44.9 (−72.0 ∼ −17.9) min for ESI level 2 and −104.3 (−114.7 ∼ −94.0) min for ESI level 3. Conclusions The TRACT protocol decreased the ED mortality in ESI 1 group and reduced the ED LOS in ESI levels 2 and 3 groups.