In this paper, a differential-fed dual-band slot antenna with end-fire radiation is proposed. The dual-band characteristic is realized with help of three resonant modes of the λ/4 slot antenna, namely, the first odd mode in the lower band and the second and third odd-mode for the higher band. By symmetrically introducing two slot stubs around the nodal lines of electric-field distributions of the third odd mode, its resonant frequency gradually moves close to that of the second odd-mode. Thus, the bandwidth of the upper operating band could be significantly improved under operation of the second and third odd modes. To validate these predicted performances, a prototype antenna is in final fabricated and tested. The operating bandwidth of the antenna is about 4% in the lower band and 24% in the upper band. Both the simulated and measured results are provided with good agreement.