Abstract: Data classification is a form of data analysis that can be used to extract models describing important data classes. There are many classification algorithms but decision tree is the most commonly used algorithm because of its ease of implementation and easier to understand compared to other classification algorithms.C4.5 is one of the most effective classification method. In this paper we are implementing this algorithm using weka data mining tool using publicly available datasets of different size. This paper also gives insights into the rate of accuracy it provides when a dataset contains noisy data, missing data and large amount of data.