NMDA receptors (NMDARs) are ionotropic glutamate receptors that mediate the flux of calcium into the postsynaptic compartment that underpins multiple forms of synaptic plasticity, learning and memory. Mice lacking functional NMDARs exhibit no long-term potentiation (LTP) in the hippocampus and display impairment in spatial memory. The majority of synaptic NMDAR currents is mediated by the GluN2A-containing heteromeric NMDARs. Although the cytoplasmic C-terminal tail of GluN2A is crucial for function, the molecular mechanisms underlying activity-dependent trafficking of GluN2A remains elusive. Recently, we identified a member of the sorting nexin (SNX) family of proteins, SNX27, as a GluN2A C-terminal interacting partner. Mutations of SNX27 gene is linked to intellectual disability, epilepsy and growth retardation. Mice lacking SNX27 display impairments in glutamatergic neurotransmission and LTP, as well as deficits in learning and memory. Here we report that SNX27 plays an important role in regulating the basal and activity-dependent forward trafficking of GluN2A-containing NMDARs in primary hippocampal neurons. SNX27 directly binds to GluN2A C-terminal tail through its postsynaptic density 95/discs large/zona occludens (PDZ) domain. Interestingly, their interaction can be modulated by the phosphorylation of GluN2A Ser-1459 residue by the Ca2+/calmodulin-dependent kinase II (CaMKII), which is enhanced by glycine stimulation that mimics LTP in vitro. Overexpression of GluN2A S1459A phosphorylation-deficient mutant significantly reduces GluN2A surface expression and activity-dependent insertion of NMDARs, whereas GluN2A S1459D phospho-mimetic mutant enhances basal GluN2A surface expression and occludes the glycine-induced enrichment of GluN2A in hippocampal neurons. Altogether, our study provides the first molecular link between GluN2A, SNX27 and CaMKII in controlling NMDAR surface expression in mammalian central neurons.