The effect of Ti on the interfacial reactions, microstructural characteristics, and the related fluidity of Al-12%B4C composites has been investigated. Without Ti addition, B4C decomposed heavily during holding, and a large quantity of reaction-induced compounds, Al3BC and AlB2, was generated. When Ti was added, a TiB2 layer was built surrounding B4C particle surfaces, which acted as a diffusion barrier to separate B4C from liquid aluminum. Thus, the decomposition of B4C slowed down remarkably. The fluidity of the composite without Ti was the shortest of all composites and deteriorated quickly during the holding time. The fluidity of the composite melt was improved significantly with increased Ti levels. The optimum Ti level for the best fluidity results lied between 1.0 and 1.5%. The solid particle volume and the particle agglomeration are the two main factors influencing the fluidity.