The present invention relates to acidic sanitizing and/or cleaning compositions comprising a specific quaternary antimicrobial system consisting of C1-C4 hydroxyalkyl carboxylic acids, C5-C18 alkyl monocarboxylic acids, unsubstituted or substituted, saturated or unsaturated C4-dicarboxylic acids and additional inorganic or organic acids. The compositions of the present invention can be present in the form of concentrates and in the form of diluted use solutions. They can be used in a process for sanitizing and/or cleaning hard surfaces, preferably in a cleaning-in-place (CIP) and/or sanitize-in-place (SIP) process for cleaning and/or sanitizing plants in the food, dairy, beverage, brewery and soft drink industries.