Recently, room-temperature flexible gas sensors have been widely studied because they can operate without being heated and create low-cost, low-power-consumption devices with long-term stability. Here, by designing the active material composition and structure, we report an electrospun carbon nanofiber (CNF) network grafted by two-dimensional MoS2 nanosheets and embedded CoS2 nanoparticles, which serves as a flexible gas sensor for various toxic or hazardous gases working at room temperature. In particular, the CNFs/CoS2/MoS2 hybrid films exhibit very high selectivity toward NO over other gases including NO2 and CH4, with selectivity coefficients (vertical bar S-NO/S-NO2 vertical bar and vertical bar S-NO/S-CH4 vertical bar) as high as 43 and 42 (defined as the ratio of responses between two gases). The sensor shows a linear relationship in the gas concentration range of 1-100 ppm and a stable response during repeated bending. Theoretical calculations suggest that MoS2 can be selectively n-doped by NO, while CoS2 can effectively capture NO molecules, leading to enhanced selectivity and sensitivity. Our large-area flexible sensors made by synergistic design have potential applications in biological and environmental areas for low-cost, selective detection of toxic or targeted gases.