Spinal motor neurons (MNs) are a highly specialized type of neurons that reside in the ventral horns and project axons to muscles to control their movement. Degeneration of MNs is implicated in a number of devastating diseases, including spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS), Charcot-Marie-Tooth and poliomyelitis disease. The above disease iPSCs have been generated from patients and attempts have been made to identify disease-related phenotypes and to dissect out the underlying mechanisms before embarking on drug discovery. using a combination of small molecules in a chemical defined neural medium, we have guided hPSCs to a near-pure population of OLIG2 þ MNPs in 12 days, and a highly enriched population of functionally mature MNs (490%) in another 16 days by the use of a Notch inhibitor. Furthermore, our approach enables expanding a single MNP to 1 104 MNPs, producing a large quantity (5 105) of consistent MNs from a single stem cell. MNs generated by this method display molecular phenotypes of SMA and ALS, and can be readily adapted to screening platforms.