Spikar is a drebrin-binding protein, which is localized in nucleus and dendritic spines in neuron. In nucleus, spikar functions as a transcriptional co-activator for nuclear receptors such as estrogen receptor. Meanwhile, spikar is involved in spine formation in cytoplasm. Overexpression of cytoplasmic spikar (mNLS-spikar), which is mutated in nuclear localization signal, actually resulted in increase of dendritic spine and filopodium in cultured neurons. However, drebrin knockdown abolishes the mNLS-spikar-induced in-crease in spine and filopodium density, suggesting that drebrin is responsible for the formation of spines and filopodium facilitated by cytoplasmic spikar. In this study, we investigated how drebrin regulates cytoplasmic spikar by using live cell imaging. We employed fluorescent recovery after photobleaching (FRAP) to evaluate the stability of spikar in dendritic spines. Cultured neurons were transfected with GFP-mNLS-spikar and drebrin-shRNA vector or negative-shRNA vector. In drebrin-knockdown neurons, the stable fraction of mNLS-spikar was smaller than that of control neurons. It suggests that drebrin functions in stabilization of spikar in dendritic spines. Further we analyzed a FRAP curve of spikar-delta-N mutant, which lacks N-terminal region containing drebrin-binding region. The results showed that the stable fraction of spikar-delta-N was much smaller than that of drebrin-knockdown neurons. It suggests that other factors such as other binding proteins including importin are involved in spikar stability in dendritic spines.