The binary offset carrier (BOC) modulation has attracted much attention as a new physical layer implementation for satellite communication and global navigation satellite systems. In this paper, we propose a new correlation function for sine-phased BOC signals. Specifically, we separate a sub-carrier pulse into several rectangular pulses, and then, generate a number of partial correlation functions. Finally we combine the partial correlation functions to yield an unambiguous correlation function with no side-peak. From numerical results, it is demonstrated that the proposed correlation function provides a significant tracking performance improvement over the conventional correlation functions.