Electronic Journal of Differential Equations, Vol. 2012 (2012), No. 159, pp. 1-6. Title: Dirichlet-to-Neumann operator on the perturbed unit disk Authors: Hassan Emamirad (Inst. for Research in Fundamental Sciences, Iran) Mohamed-Reza Mokhtarzadeh (Inst. for Research in Fundamental Sciences, Iran) Abstract: This article concerns the Laplacian on a perturbed unit disk $\Omega_\epsilon=\{ z=r\exp(i\theta): r <1+\epsilon f(\theta) \}$, with dynamical boundary condition whose solution can be represented by a Dirichlet-to-Neumann semigroup. By neglecting the terms of order $\epsilon^2$, we obtain a simple expression which allows us to use Chernoff's theorem for its approximation. As a motivation for this research, we present an example which shows the feasibility of applying Chernoff's Theorem. Submitted June 19, 2012. Published September 18, 2012. Math Subject Classifications: 35J25, 47F05, 47D06. Key Words: Dirichlet-to-Neumann operator, gamma-harmonic lifting.