With excellent beam quality, high wall-plug efficiency, low maintenance costs, long lifetime of pump diodes, flexible beam delivery and compact size, the new fiber lasers are very attractive for welding and cutting various kinds of materials in industrial applications since the short wavelength laser beams can be absorbed by almost all metals and alloys. Fiber laser- metal inert gas (MIG) hybrid welding is carried out onto TC4 alloy. The effects of laser-leading (LL) and arc-leading (AL) welding direction on top bead appearance, cross section, penetration depth, width and reinforcement of welds are investigated. The results show that the fiber laser-MIG hybrid welding in LL welding direction leads to better top bead appearance, wider weld width and shallower penetration depth, than those in AL welding direction. The weld direction has little influence on the reinforcement of the welds.