A novel Koch fractal printed Yagi-Uda antenna fed by coplanar waveguide (CPW) is proposed and analyzed. The antenna has flrst-order Koch fractal monopoles, and the monopoles' ground plane acts as the ground plane of the antenna. The radiation characteristics of the antenna are simulated by CST Microwave Studio r and explained by the simulated results. The antenna's currents distribution becomes more uniform after being fractal, which is conducive to increasing antenna's radiation directivity. The proposed Koch fractal Yagi-Uda antenna has an operating band of 885{913MHz (relative bandwidth 3.1%) with the center frequency of 900MHz. The total antenna size is 171mm £ 85mm (0.51‚ £ 0:25‚) and the length in the antenna's polarization direction is only 25% of the wavelength corresponding to the center frequency. Compared to traditional Yagi-Uda antenna, the proposed antenna can achieve a 50% miniaturization efiect.