A novel omnidirectional antenna with the null-filled radiation pattern is proposed in this work. The designed antenna can fill the inherent blind zone at the zenith of a traditional monopole antenna and, meanwhile, maintain good omnidirectional radiation characteristics in the horizontal direction. A metallic ring connected to the monopole antenna is utilized to adjust the original current distribution so that the elimination of the blind zone can be achieved. Furthermore, a ring slot is opened centering on the ground plane to improve the radiation capability of the antenna in the horizontal direction. The measured s11 of the antenna is better than -10 dB in 3.4-6.0 GHz, achieving a relative bandwidth of 54.9%. The zenith gain of 0.8 dBi and the lowest H-plane radiation gain of -0.4 dBi are obtained. The measured and simulated results are in good agreement, effectively verifying the feasibility of the proposed antenna in practical applications.