Neural adhesion molecule NB-3 plays an important role in the apical dendrite development of layer V pyramidal neurons in the visual cortex, and receptor-like protein-tyrosine phosphatase alpha (PTPalpha) mediates NB-3 signaling in this process. Here we investigated the role of PTPalpha in regulating cell surface expression of NB-3. We found that cortical neurons from PTPalpha knock-out mice exhibited a lower level of NB-3 at the cell surface. When expressed in COS1 cells, NB-3 was enriched in the Golgi apparatus with a low level of cell surface expression. However, co-expression of PTPalpha increased the cell surface distribution of NB-3. Further analysis showed that PTPalpha facilitated Golgi exit of NB-3 and stabilized NB-3 protein at the cell surface by preventing its release from the plasma membrane. The extracellular region of PTPalpha but not its catalytic activity is necessary for its effect on NB-3 expression. Thus, the PTPalpha-mediated increase of NB-3 level at the cell surface represents a novel function of PTPalpha in NB-3 signaling in neural development.