Alpha-case formations between investment molds and TiAl alloys were investigated for economic TiAl alloys net-shape forming. The α-case reactions between mold and TiAl alloys were characterized by using optical microscopy and a hardness tester. In the case of TiAl alloys, there were no α-case formation reactions. The α-case was formed not only by interstitial oxygen elements but also by substitutional metallic elements dissolved from mold materials. There were neither interstitial nor substitutional α-case formations since TiAl alloys have both negligible solubility of oxygen and low activity in molten states. The results of the investment casting of TiAl alloys confirmed that the casting route in our study can be an effective approach for the economic net-shape forming of TiAl alloys automotive parts.