The process of urban growth is closely related to the size distribution of cities. The distribution of urban population takes place among settlements of differing sizes along a continuum from small towns to giant cities. The mono–centric urban structure becomes monocentered and dominates the rest of the urban system. The study of urban growth by size class of towns will help us to understand the changes of urban development in a region. To describe the size distribution of cities, we use Zipf‘s law, which states that the size distributions of cities follow a simple Pareto distribution with shape parameter equal to 1. In this paper we have performed a test for Zipf‘s law census data for Kerala‘s city and town sizes distribution for the period 1951 – 2001. The analysis of data reveals that class I and Class II towns dominates the urban system in Kerala in terms of their share in urban population. An indepth study of the City Size Distribution demonstrated that the value of Pareto coefficient is approximately equal to1 for the full data and for the different sample threshold population.