In this letter, a planar endfire filtering antenna with a controllable passband and a high gain based on spoof surface plasmon polaritons (SSPPs) is proposed. Its radiating part consists of three pairs of sector-shaped patches and I-shaped directors which are linked with the end of SSPPs feeding line. As demonstrated, the filtering performance of the proposed antenna can be easily adjusted by changing the size of all the branches with metal vias, round-shaped, and π-shaped resonators. A prototype operating in 8-9 GHz is fabricated and tested to verify the design, which reveals an average gain of 8.6 dBi, an out-of-band suppression level of more than 12 dB, and a profile of 0.014-λ0. Good agreement is achieved between the simulated and measured results. Simple and controllable design methods and good performance indicate its significance in modern communication systems.