Smartphone app market is getting important socially and economically. As damage of app piracy increases, we require a technique to encourage purchase and use of legal apps. Digital Rights Management (DRM) for apps such as Google’s LVL and SKT's ARM is studied and used. They are techniques based on user authentication. But they are easy to circumvent because Smartphone apps are weak to reverse engineering and modification. In this paper, we propose a technique that enforces the existing techniques to solve the above problems. This technique use class separation and class dynamic loading. The technique separates a particular class when developing apps and servers must keep it. After user authentication on every run, the separated class is transferred from the server and dynamically loaded. Experimental results show the technique is feasible on Smartphone environment.