© 2022 IEEE.In this paper, we investigate channel estimation performance on sum-rate for reconfigurable intelligent surface (RIS) assisted unmanned aerial vehicles (UAV)-based multiple-input single-output (MISO) systems with multi-users. We assume that a drone with a predetermined trajectory acts as a base station. The channel estimation is performed by PARAllel FACtor (PARAFAC) decomposition method. Sum-rate simulations are performed for the cases where the channel is perfectly known and unknown. From the simulation results, it has been observed that the number of pilot signals used for channel estimation is quite effective on the total transmission speed as it improves the channel estimation.