Provided herein are novel base modified bicyclic nucleosides, oligomeric compounds prepared therefrom and methods of using the oligomeric compounds. More particularly, novel pyrimidine bicyclic nucleosides are provided wherein each pyrimidine base is substituted at the 5 position with an optionally substituted, aromatic or heteroaromatic ring system comprising from 5 to 7 ring atoms selected from C, N, O and S. In certain embodiments, the oligomeric compounds provided herein hybridize to a portion of a target RNA resulting in loss of normal function of the target RNA.
