Mechanical properties of as-cast beta titanium (β-Ti) alloy can be improved by grain refinement and formation of insoluble precipitate. This paper reports the effect of carbon (C) addition on microstructure and hardness of cast Ti–15V–3Cr–3Sn–3Al (Ti-15-3) samples prepared by argon arc melting. X-ray diffraction analysis of C added as cast Ti-15-3 samples revealed the presence of β-Ti and TiC phases. Scanning electron microscope analysis revealed eutectic TiC precipitates in C added Ti-15-3 samples while a reduction in grain size was observed with increasing carbon addition. Inoculation effect due to TiC and growth restriction by C for β phase resulted in decreased grain size. Hardness of C added Ti-15-3 alloys increased with the increased carbon content of the sample. The improvement in hardness was contributed by grain refinement and the formation of TiC precipitates in the samples.