A low-profile half-mode substrate integrated waveguide (HMSIW) filtering antenna with high frequency selectivity is proposed in this letter. The proposed antenna with a height of 0.014λ0 (λ0 is the free-space wavelength) consists of a slot-loaded HMSIW cavity, two parasitic patches, and five shorting pins. An upper-edge radiation null is generated by the interaction between the HMSIW cavity and parasitic patches. A rectangular slot etched on the HMSIW cavity is adopted to generate another null to improve the filtering performances at the upper stopband. Besides, the radiation in the lower stopband is suppressed by two nulls which emerge due to placing shorting pins under two parasitic patches. Thus, four radiation nulls can be obtained to enhance the frequency selectivity. The measured results illustrate that the proposed antenna provides an impedance bandwidth of 4.3% ranging from 2.74 to 2.86 GHz and a peak gain of 6.76 dBi during the operating frequency band. Moreover, four radiation nulls appear at 2.34, 2.56, 3, and 3.24 GHz in the lower and upper stopbands.