We construct the homotopy pullback of A n -spaces and show some universal property of it. As the first application, we review the Zabrodsky's result which states that for each prime p, there is a finite CW complex which admits an A p−1 -form but no A p -form. As the second application, we investigate A n -types of gauge groups. In particular, we give a new result on A n -types of the gauge groups of principal SU(2)-bundles over S 4 , which is a complete classification when they are localized away from 2.2010 Mathematics Subject Classification. 54C35 (primary), 18D50, 55P45, 55R10 (secondary).