An omnidirectional dual-polarized antenna with high port isolation is presented for 2.4-GHz wireless local area network (WLAN) applications. The omnidirectional patterns of both vertical and horizontal polarizations in the azimuthal plane are achieved by positioning two orthogonal slots cut onto the walls of a slender columnar cuboid. The overall volume of the proposed antenna is only 83 × 11 × 11mm3 (0.664λ0 × 0.088λ0 × 0.088λ0), with low mutual coupling between two radiating slots. A prototype of the proposed antenna is fabricated and tested. The measured results show that the 10-dB reflection coefficient bandwidths of dual polarizations cover the desired band of 2.4-2.48 GHz and the port isolation is lower than -33.5 dB. Stable gains are greater than 3.17 and 1.19 dBi for vertical and horizontal polarizations, respectively. The diversity performance is also evaluated, including the correlation coefficient, mean effective gain (MEG) ratio, and diversity gain.