Ti-Al-Nb based alloys were prepared by a non consumable skull melting. The effect of Al content on the microstructure and the solidification characterization of as-cast alloys were investigated using X-ray diffraction, optical microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that a fine grain structure Ti-44Al-2Nb-1Cr-1W-1B alloy with average grain size 50 mm could be got by proper decreasing of Al content, and the companion phenomenon of co-existence of b and g phases in the fine grain structure as-cast alloy was found. Moreover, the proper additions of alloying elements such as W and Nb increased the stability of b phase, and thus b phase was retained to low temperature. The presence of b phase was found to restrict a grain growth at the temperatures above the a transus temperature.