This paper has proposed an end-fire slot antenna with back-lobe level suppression and front-to-back ratio (FBR) improvement. At first, the radiation characteristic of the conventional λ/4 slot antenna are meticulously investigated to initially demonstrate that its FBR can be maintained as high as about 6 dB. Then, the antenna under three different boundary conditions is deeply studied. The results reveal that the currents along the two sides of the metal ground are parallel to the slot radiator, resulting to affect the back-lobe radiation level to a great degree. As such, a pair of rectangular slots is properly etched on the two sides of the metal ground for further reduction of back-lobe radiation level and FBR improvement. Finally, a prototype antenna operating at 4.7 GHz is designed and fabricated. The measured results demonstrate that the back-lobe is indeed greatly decreased as predicted and the measured FBR of the proposed slot antenna exceeds 25 dB, where an increment of about 19 dB than the conventional λ/4 slot counterpart is successfully obtained, thereby evidently exhibiting better end-fire radiation performance.