  We present here $Spitzer$ mid-infrared (IR) spectra and modeling of the
spectral energy distribution (SED) of a selection of post-Asymptotic Giant
Branch (PAGB) stars. The mid-IR spectra of majority of these sources showed
spectral features such as polycyclic aromatic hydrocarbons (PAHs) and silicates
in emission. Our results from SED modeling showed interesting trends of
dependency between the photospheric and circumstellar parameters. A trend of
dependency is also noticed between the ratios of equivalent widths (EWs) of
various vibrational modes of PAHs and the photospheric temperature T$_{*}$ and
model-derived stellar parameters for the sample stars. The PAGB mass loss rates
derived from the SED models are found to be higher than those for the AGB
stars. In a few objects, low and high excitation fine structure emission lines
were identified, indicating their advanced stage of evolution. Further, IR
vibration modes of fullerene (C$_{60}$) were detected for the first time in the
PAGB star IRAS 21546+4721.
