The clickabilities of various alkenyl and alkyl azides in the strain-promoted cycloaddition with dibenzo-fused cyclooctynes were investigated. Although alkenyl azides generally exhibited lower clickabilities than those of alkyl azides, a sterically-hindered alkenyl azide showed high reactivity comparable with those of alkyl azides. Theoretical analyses indicated that these unique reactivities are derived from the frontier molecular orbital interactions and distortability of the azido groups.