Recently, a variety of mobile security threats have been emerged due to the exponential growth in mobile technologies. Various techniques have been developed to address the risks associated with malware. The most popular method to detect Android malware relies on the signature-based method. The drawback of this method is that it is unable to detect unknown malware. Due to this problem, machine learning came into existence for detecting and classifying malware applications. The conventional machine learning algorithms focus on optimizing classification accuracy. However, the imbalanced real-life datasets cause the traditional classification algorithm to perform poorly in classifying malicious apps. To handle the problem of imbalanced family classification of malicious applications, we propose a Cost-Sensitive Forest (CSForest) method which contains a group of decision trees. A cost-sensitive voting technique is used for prediction purposes. The proposed approach is evaluated on a dataset that includes the features extracted from both static and dynamic malware analysis and consisting of 13 imbalanced families of Android malware. Furthermore, the results of proposed technique are compared with the C4.5, Random Forest and CSTree to determine its effectiveness in classifying the families of malicious applications while considering only static features, only dynamic features and their hybrid. From the experimental results, it is found that CSForest performs better than the other algorithms in handling the imbalanced family classification of Android malicious applications while considering the hybrid set of features. It acquires the highest F-measure rate i.e. 0.919 with a minimum total cost of 180. © 2021, Bharati Vidyapeeth's Institute of Computer Applications and Management.