Diabetes is a major health problem around the world. In vitro enzyme-based glucose test strips have dominated the self-monitoring of blood glucose; however, the pain associated with fingerstick often deters patients from frequent monitoring. In this study, we report a subcutaneously injected surface enhanced Raman scattering (SERS) nanosensor to enable long-term in vivo glucose tracking. The glucose-responsive SERS nanosensor was prepared by self-assembling of a monolayer of 4-mercaptophenylboronic acid (MPBA) on gold nanoparticles (AuNPs). The aggregates of MPBA-functionalized AuNPs (MPBA-AuNPs) resulted in Raman signal enhancement of MPBA, and thus endowed MPBA-AuNPs serving as functional SERS nanosensor for glucose monitoring. After the demonstration of in vitro and ex vivo glucose detection, the glucose-responsive SERS nanosensor was subcutaneously injected into nude mice to investigate its ability in long-term in vivo glucose tracking. The trends obtained from glucose monitoring using a portable Raman probe in mice show a reasonable match with the ones derived from blood using a commercial glucose meter over a period of 60 days. The good biocompatibility of the subcutaneously injected MPBA-AuNPs nanosensor was also validated through histological analysis. All these features indicate that the as-prepared SERS nanosensor holds great potential in long-term glucose tracking.