Neuronal cells possess dendritic and axonal processes, and through these processes they form neuronal circuits in the brain. To elucidate the neuronal circuits, it is indispensable to visualize both the cell bodies of neurons as well as their processes. Although there are several methods for visualizing these processes, such as immunostaining and intracellular staining, labeling with recombinant virus vectors has become a powerful tool because reporter proteins can be expressed in infected cells. Among the available vectors, the lentivirus vector shows low cytotoxicity, and its genome can be integrated into the genome of infected cells, resulting in stable transgene expression. Using this vector, we previously developed a reporter protein anchored to the somatodendritic membranes of neurons. The reporter protein clearly visualizes the contours of dendritic shafts and spines, which preferentially receive excitatory synaptic inputs and show morphological changes associated with synaptic activity. In this chapter, the detailed protocol for the production, purification, and injection of lentivirus vectors is described. Subsequently, the clear visualization of dendritic spines of the neurons in the neocortex and caudate-putamen is demonstrated.