Current cloud computing systems pose serious limitation to protecting users' data confidentiality. Since users' sensitive data is presented in unencrypted forms to remote machines owned and operated by third party service providers, the risks of unauthorized disclosure of the users' sensitive data by service providers may be high. Many techniques for protecting users' data from outside attackers are available, but currently there exists no effective way for protecting users' sensitive data from service providers in cloud computing. In this paper, an approach is presented to protecting the confidentiality of users' data from service providers, and ensures that service providers cannot access or disclose users' confidential data being processed and stored in cloud computing systems. Our approach has three major aspects: 1) separating software service providers and infrastructure service providers in cloud computing, 2) hiding information of the owners of data, and 3) data obfuscation. An example to show how our approach can protect the confidentiality of users' data from service providers in cloud computing is given. Experimental results are presented to show that our approach has reasonable performance.