We measured synchronization performance of FlexRay for OSEKtime and described why we must consider synchronization performance. Previous studies present scheduling methods for time-triggered systems when ideal constraints WCET(Worst Case Execution Time), deadline, resource dependency, etc.) are given. However, there are some differences between real distributed systems and ideal constraints. Because the scheduling method of OSEKtime is based on a clock that is synchronized via a communication protocol such as CAN (controller area network) and FlexRay, synchronization performance influences the scheduling result. Therefore, we measured the synchronization performance of FlexRay and described why we must consider synchronization performance for OSEKtime scheduling.