The complexity of ES continues to grow in terms of integration of multiple technologies, component count, expected performance and security constraints. In addition, the design of this type of system must be set properly taking into account all necessary elements in order to ensure a safe and secure system. Good design means a good choice of modeling language. In this paper, we present two modeling languages UML and SysML. We will show the limitation of UML when modeling Embedded Systems. In the same time, we prove the effectiveness of SysML language. We illustrate this result with a clear example of an Embedded System which is a cellular phone.