A thin-film waveguide amplifier based on Er-doped Garnet crystals is proposed and transient amplification characteristics, studied numerically using time-dependent rate equations and mode evolution equations, are presented. The potential of the amplifier for integration with active devices operating at the present communication wavelength of 1. 53 µm band is revealed. Pump wavelengths in the visible and near infrared lead to excited state absorption, and will affect the gain characteristics, which has been included in the present study. Steady state response of the Er doped Garnet crystal waveguide amplifiers has been analyzed in order to optimize the gain characteristics, which are further used in the dynamic response analysis. Accordingly, it is shown that a high gain of 20 dB/cm is possible to be achieved. Experimentally determined parameters such as waveguide loss, absorption and emission cross-sections have been used for the simulations. Comparisons of the present simulation results with our earlier reported results of quasi-two-level laser model and other reported results are also presented. Understanding the dynamic characteristics of the integrated optic waveguide amplifiers is necessary when the input signal is modulated in various formats. Because of the slower gain dynamics of the Er doped Garnet amplifier medium, it is shown that the longer signal input pulses are observed to be distorted upon amplification. Very short single pulse of nano- and pico-second duration are amplified without change in the pulse shape. Input pulses of square, Gaussian and Lorentzian shapes have been considered for the numerical examples.