Abstract: The invention provides a process and composition of low toxicity for prepng aluminum surfaces for adhesive bonding. The process involves treating the aluminum with an etching composition composed of sulfuric acid, ferric sulfate and water. The invention eliminates the toxicity and pollution problems associated with the conventional chromate-type etching baths, reduces the contamination of the work place and environment to acceptable levels, and produces aluminum surfaces, which when adhesively bonded yield joints comparable in strength to those obtained by use of the conventional chromate-type etchant bath.