Motoneurons (MNs) derived from mouse embryonic stem cells (ESCs) begin to express low levels of polysialic acid (PSA) at the time when they acquire an ability to migrate and extend neurites. PSA is known to promote cell migration and process outgrowth/guidance in the developing nervous system. To test if experimentally enhanced expression of PSA would augment these cellular events, the PSA-synthesizing polysialyltransferase was introduced into ESCs. In culture, the resulting higher PSA expression specifically increased neurite outgrowth and cell migration from differentiated embryoid bodies. In addition, the MN population obtained after sorting for HB9::GFP expression showed enhanced survival as well as extensive neurite outgrowth. Following transplantation of ESC-derived MNs into an adult sciatic nerve devoid of endogenous axons, the PSA augmentation increased the numbers of axons growing toward the denervated muscles. Migration of some transplanted cells inside the nerve toward muscle was also enhanced. Moreover, higher PSA expression selectively affected target innervation. It produced greater numbers of neuromuscular junctions in a predominantly fast twitch muscle and had no effect in a slow twitch muscle. These findings suggest that engineering of PSA expression in ESC could serve as an enhancement for MN cell therapy.