Background: The impact of Certificate of Need (CON) law on Emergency Department (ED) care remains elusive in the academic literature. Objectives: We study the impact of CON law on ED Length of Stay (LOS). Methods: We examine ED LOS to detect any statistically significant difference between CON and Non CON states. We then estimate the effects of CON law on ED LOS by treating CON as an exogenous (endogenous) variable. Results: We find that CON legislation positively impacts ED care by reducing ED LOS (95% confidence interval [CI]: -61.3, -10.3) and we can’t reject the hypothesis that CON legislation can be treated as an exogenous variable in our model. An increase in the stringency of the CON law (measured by the threshold on equipment expenditure that is subject to a CON review) tends to diminish this positive impact on ED LOS (95% [CI]: 9.9, 68.0). The party affiliation of the governor (95% [CI]: 10.3, 37.5), the political environment as a function of the agreement on voting between state senators (95% [CI]: -64.8, -12.9), proportion of young population (0-17 years) when compared with the elderly (>65 years) (95% [CI]: -2299.7, -184.1), proportion of population covered by privately purchased insurance (95% [CI]: -819.3, -59.9), etc., are found to significantly impact ED LOS in a state. Conclusion: This study provides a better understanding of the impact of CON law on ED care, which extends the previous literature that has mainly focused on CON effects on inpatient care.