The sensitivity of two-dimensional isothermal film casting processes to ongoing sinusoidal disturbances has been investigated by using the frequency response method with transient simulation techniques. Amplitude ratios of state variables such as cross-sectional area, film width and film thickness at the take-up position with respect to a sinusoidal disturbance show resonant peaks along the frequency domain. Effects of operating conditions, such as drawdown ratio and aspect ratio, on the process sensitivity have been examined. Increasing drawdown ratio and decreasing aspect ratio make the system more sensitive to disturbances. Also, the dichotomous behavior in the sensitivity analysis using viscoelastic Phan-Thien and Tanner fluids has been elucidated. This frequency response method can be a useful tool to optimally design process systems for better processability and product quality.