A novel one-pot synthesis of N-acylindoles via tandem cycloalkylation-annelation is described. This approach is based on the use of a strong solid-acid catalyst, montmorillonite K-10, and microwave irradiation under solvent-free conditions. The tandem cycloalkylation of amides and annelation of intermediate pyrroles were completed in minutes and provided good yields with high selectivities for the indoles. The safe, easy to handle catalyst, and the convenience of the product isolation make this process an attractive, environmentally benign alternative for the synthesis of N-acylindoles.