MXene, a new kind of two-dimensional (2D) materials, has unique combination of excellent physical and chemical properties. Via computations on density functional theory and deformation potential theory, we investigated the electronic structure and predicted the carrier mobility of Ti 2 CO 2 (a typical MXene) monolayer and nanoribbons. Ti 2 CO 2 monolayer is a semiconductor with a band gap of 0.91 eV, and the hole mobility in the monolayer reaches 10 4 order of magnitude along both x and y direction, which is 10 much higher than that of MoS 2 , while the electron mobility is about two orders of magnitude lower. The dramatic difference between hole and electron mobility also exists in nanoribbons. Moreover, our results suggest that width controlling and edge engineering would be effective in adjusting the carrier mobility of Ti 2 CO 2 nanoribbons, and endow experimentally available Ti 2 CO 2 with wide applications to field-effect transistors and photocatalysts. 15