The production of tritium from a lithium blanket with a vanadium alloy structure was predicted using the MCNP. The model was designed to include a lithium breeder, reflector, shielding and structure. Different forms of lithium, including natural lithium, FLiBe and LiPb, were considered. LiPb had the highest tritium production per source neutron among the three forms of lithium considered. In addition, it was found that the concentration of $^6$Li in the liquid lithium strongly affected tritium production from the model blanket. With 75 percent $^6$Li enrichment in the LiPb, the overall tritium production in the breeder zone was about 8 particle/cm$^2$/source neutron, which was more than two times of that using natural lithium. Moreover, the tritium production rate reduced up to 15% when the 2-cm thick of tungsten was added in front of the breeding zone as a first wall material.