Polycarbosilanes with SiH2 units in the main chain may undergo diverse reactions to access a family of functionalized polymers with enhanced added values. However, the preparation of such polymers has been hampered by uncontrollable side reactions involving Si-H bonds under transition-metal-catalyzed conditions. We described here the first selective bis-hydrosilylation of dienes with bis(hydrosilanes) enabled by rare-earth-metal catalysts to yield linear polycarbosilanes with SiH2 units in the chain. The SiH bonds in the polymers could undergo halogenation, Si-O coupling, and hydrosilylation to yield a family of functionalized polycarbosilanes.