This paper investigates the achievable rate maximization problem of a downlink unmanned aerial vehicle (UAV)-enabled communication system aided by an intelligent omni-surface (IOS). Different from the state-of-the-art reconfigurable intelligent surface (RIS) that only reflects incident signals, the IOS can simultaneously reflect and transmit the signals, thereby providing full-dimensional rate enhancement. We formulate this rate maximization problem by jointly optimizing the IOS’s phase shift and the UAV trajectory. Although it is difficult to solve it optimally due to its non-convexity, we propose an efficient algorithm to obtain a high-quality suboptimal solution. Simulation results show that the IOS-assisted UAV communications can achieve significant improvement in achievable rates compared to other benchmark schemes.