The present technology provides aryl or heteroaryl triazolone derivatives or pharmaceutically acceptable salts thereof, preparation processes thereof, pharmaceutical compositions comprising the same, and the use thereof. The aryl or heteroaryl triazolone derivatives or their pharmaceutically acceptable salts exhibit selective inhibitory activity on VAP-1 and therefore can be usefully applied, e.g., for the treatment and prophylaxis of nonalcoholic hepatosteatosis (NASH).