  We have derived Earth Similarity Index (ESI) with two free parameters m and
T. These free parameters are optimized with the consideration that the planet
Mars is almost similar to the Earth. For the optimized values of free
parameters, the interior-ESI, surface-ESI and ESI for some planets are
calculated. The results for m = 0.8 and T = 0.8 are compared with the values
obtained by Schulze-Makuch {\it et al.} (2011). We have found that the
exoplanet 55 Cnc f is within 10% away from the threshold value T. The
exoplanets HD 69830 c, 55 Cnc c, 55 Cnc f, 61 Vir d and HIP 57050 b are found
to have ESI within 10% from the threshold value.
