The purpose of this study was to investigate the feasibility of developing transdermal drug delivery system for ketotifen used for asthma, allergic conjunctivitis, and rhinitis. The permeation of ketotifen in silicone, polyisobutylene, styrene-butadiene-styrene and acrylic-rubber hybrid and acrylic pressure sensitive adhesive matrix was evaluated. Due to good adhesion force and high permeability, acrylic-rubber hybrid adhesive was chosen. Permeation rate was found to increase linearly as the drug concentration in acrylic-rubber hybrid adhesive increased. However, when the drug concentration was 5 % or more in the matrix, recrystallization of ketotifen was observed. The recrystallization process was not inhibited by crystallization inhibitors tested. Significant increase in flux was obtained using Brij$^{(R)}$ 30, Crovol$^{(R)}$ A40, Span$^{(R)}$ 80 and Lauroglycol$^{(R)}$ FCC as permeation enhancers.