The present invention discloses a pair of differential microstrip lines with low cross-talk for high-frequency signal transmission. The pair of microstrip lines comprises two microstrip lines. The first microstrip line is used to transmit the first transmission signal. The second microstrip line is parallel to the first microstrip line and used to transmit the second transmission signal. The first transmission signal is the complementary signal of the second transmission signal and has a 180° phase difference from the second transmission signal. Particularly, there are a plurality of slots periodically arranged on the outer sides of the first and the second microstrip lines to form a subwavelength configuration. The subwavelength configuration is to make the periodical arrangement length of these slots shorter than the wavelengths of the first and the second transmission signals. These slots can provide subwavelength confinement for enhancing electromagnetic wave.