AMPA receptors (AMPAR) auxiliary subunit TARPγ-8 is a critical molecule for recruiting AMPAR to hippocampal excitatory synapses. Although biochemical interaction of TARPγ-8 with PSD95 has been reported, it is not fully understood how the TARPγ-8-PSD95 interaction contributes to the distribution of TARPγ-8. Here we aimed to reveal the distribution of TARPγ-8 in neurons and to examine the effect of TARPγ-8-PSD95 coupling on spatiotemporal dynamics of TARPγ-8. First, we confirmed that TARPγ-8 was accumulated at the synapse in cultured neurons by immunostaining. Then we examined the effect of PSD95 on the intracellular distribution of TARPγ-8 by heterologous expression of fluorescent protein tagged constructs in COS7 cells. TARPγ-8 and PSD95 formed molecular clusters with the typical size of ~1 μm, while TARPγ-8 solely expressed in cells showed diffuse pattern. Furthermore, we performed single-particle tracking of TARPγ-8, revealing that the TARPγ-8 molecules within the clusters were in an immobile state with the diffusion coefficient (D) of less than 0.01 μm²/s, while the TARPγ-8 molecules outside the clusters were highly mobile with D of ~0.05 μm²/s. Our results suggest that PSD95 assemblies regulate the dynamics of TARPγ-8, and that PSD95-TARPγ-8 coupling plays a functional role in recruiting AMPAR to the synaptic membrane.