Three-component coupling (3CC) of indoles, aldehydes, and N-alkylanilines has been accomplished using a catalytic amount of cellulose-sulfonic acid under mild reaction conditions to furnish the 3-aminoalkylindoles at room temperature in short reaction times and in relatively good to excellent yields and selectivity. The use of biodegradable cellulose-sulfonic acid makes this method quite simple, convenient, and economically viable for the synthesis of 3-aminoalkylindoles.