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Nb-21Ti-4C (βNb-Ti) alloys with different Al contents were fabricated by a vacuum non-consumable arc-melting method. The effects of Al content on the microstructure and lattice parameters of the alloys were studied. The results indicate that the as-cast alloys contain dendritic-growth niobium solid solution Nbss, carbide (Nb, Ti)C, Nb3Al and interdendritic eutectic of Nbss/MC. The nucleation and growth of Nb3Al are in dendritic Nbss, and other Al elements dissolve into Nbss and MC. The Nbss dendritic size increases first and then decreases with Al content increasing. After heat treatment at 1100 oC for 24 h, Nbss of interdendritic eutectic grows further as a discontinuous precipitation process, and needle-like or plate-like MC and Nb3Al precipitate from Nbss, resulting in lattice parameters becoming larger; the lattice parameters of MC changes with Al content change and Nb precipitation.