Microstructure and hardness of Two β TiAl alloys, with nominal composition of Ti-42.5Al-2Cr-0.2W-3Ta and Ti-42.5Al-2Cr-0.2W (at.%), were investigated. Both as-rolling and heatreated alloys were examined by optical and scanning electron microscopy and transmission electron microscopy. As-rolling, the lamllar were coarse and the α grain enriched inTi-42.5Al-2Cr-0.2W alloy. Tantalum additions were effective in grain refinement, recrystal grains enriched and the α grain depleted in the microstructure. When the heatreatment temperature increased, the lamellar colonies globularizated more, metastable β phases decomposited as α2+γ.And the time increased, the lamella grain and the γ grain also increased rapidly and respectively in Ti-42.5Al-2Cr-0.2W alloy . The microstructure of the sheet with Ta contained more β phases than the sheet without Ta. Meanwhile, the ω phase precipitated in the alloy with Ta. Besides, the value of hardness for the alloy with Ta was lower than the alloy without Ta, for the Tantalum was effective in grain refinement, the number of β phases and ω phases was few in microstructure.