This letter presents a printed wideband linear-to-circular polarizer for X-band applications. The proposed polarizer consists of a periodic array of orthogonally inserted slot-line structures, which are treated as two independent transmission paths for two orthogonal components of a linearly polarized incident plane wave, respectively. In order to effectively realize linear-to-circular polarization conversion, the orthogonal slot-line structures are loaded with inductive strips and pairs of open-circuited strips, respectively. This arrangement can maintain equal magnitude and 90° phase difference between these two transmission paths in a wideband frequency range. With the aid of equivalent circuit models, an operation principle of the proposed polarizer is extensively explained, and a design example is then conducted based on the prescribed specifications. Finally, the designed polarizer is fabricated and measured. The measured results confirm the theoretical predictions that the insertion loss is less than 1 dB from 8.27 to 13 GHz, and the axial ratio is less than 1 dB over entire band ranged from 7.92 to 12.16 GHz. This kind of polarizer indeed features great design flexibility, low insertion loss, and wide polarization conversion bandwidth.