For the purpose of efficient and safe transdermal administration of propranolol hydrochloride (PHCl), effects of (+)-borneol, (+)-camphor, and ${alpha}$-bisabolol (5 w/v%) in 66.6% ethanol solution on transdermal permeation across rat skin in vitro and their enhancement mechanism was investigated with fourier transform infrared spectroscopy, differential scanning calorimetry, and PHCl-stratum corneum binding studies. Each of (+)-borneol, (+)-camphor, and ${alpha}$-bisabolol significantly increased the transdermal flux of PHCl through rat skin in comparison to the control. The enhancement mechanism of the terpenes is involved with disruption of the lipid bilayer and increase of PHCl partitioning coefficient to the stratum corneum. As for ${alpha}$-bisabolol, the protect effect of skin from dehydration and an important reason of irritation incident were observed with differential scanning calorimetry for the first time.