This paper reports efficient and selective silanolytic (PhSiH3, n-BuSiH3, C6H5CH2SiH3) chain transfer in organolanthanide-catalyzed homogeneous ethylene polymerization and ethylene copolymerization with several alpha-olefins. The result is st series of silyl-capped polyolefins which have been characterized by H-1/C-13 NMR and IR spectroscopy as well as by GPC. In [(Me5C5)(2)LnH](2)/[Me2Si(Me4C5)(2)LnH](2)-mediated ethylene homopolymerization and ethylene copolymerization, both primary arylsilanes (PhSiH3) and alkylsilanes (n-BuSiH3, C6H5CH2SiH3) function as efficient chain-transfer agents. In the case of ethylene polymerization mediated by [(Me5C5)(2)SmH](2), the mechanism of chain transfer is supported by the observation that M-n of the capped polyethylenes formed at constant [catalyst], [PhSiH3], [ethylene] is inversely proportional to [PhSiH3]. Using silane-activated Me2Si(Me4C5)(2)LnCH(SiMe3)(2) precatalysts, this chain-transfer process also efficiently produces silyl-endcapped ethylene + l-hexene copolymers and ethylene + styrene copolymers.