A novel dendrite splitting phenomenon in as-cast TiAl alloys was observed to show microstructural morphologies as well as crystallographic characteristics similar to those of twinned dendrites. For a β-solidified TiAl alloy, the solidified dendrite is splitted in the center by a {111} plane, the parts on both sides of which follow a particular orientation relationship that resembles twinned dendrites in Al alloys. In other words, the dendrite splitting yields twinned dendrite. The formation mechanism of twinned dendrites is related to the atom attachment behaviors at the liquid-solid interface during solidification. For the TiAl alloy with the primary phase being γ, straight twinned {111} plane layers with the thickness of a few to dozens of microns form longitudinally in the center of the columnar dendrites. The same orientation relationships appear in both β- and γ-solidified TiAl alloys, although their primary phases are different. This paper provides new details involved in the solidification of TiAl alloys.