Electrosynthesis methods have been employed as a mild and facile alternative for the syntheses of polycarbosilanes. Electropolymerization was conducted on chloromethylchlorosilanes, [ClCH2Si(CH3)(3-m)Cl-m (m = 1, 2)], taking advantage of the fact that these compounds contain two types of functional groups, CH2-Cl and Si-Cl, both of which are electrochemically active with different reduction potentials. Under a constant current, -CH2Cl is preferentially reduced to a carbanion, -SiCH2:(-), that can nucleophilically attack a Si-Cl bond to form a CH2-Si linkage; branching should occur when more than one Cl atom resides on the silicon atom since each group is capable of reacting with the nucleophilic carbanion. Thus, the condition for polymerization of highly branched polycarbosilanes is m > 1. Detailed spectroscopic characterizations of the oligomers and polymers with GPC, NMR, IR, and GC-MS are given. The formation of diverse structures, molecular weights, and reaction yields is strongly dependent on the electrosynthesis conditions, such as electrode composition and supporting electrolyte (SE). Thus, high molecular weight (M-n approximate to 57 000) of highly branched but soluble poly[methylsilylenemethylene] is obtained by electropolymerization of ClCH2Si(CH3)Cl-2 with the Al/nickel (anode/cathode) pair and Bu4N+BF4 (SE). GC-MS analysis confirms that a number of oligomeric structures can be produced by electrosynthesis, and diverse structural irregularities (i.e., cross-linking, loop, and fused rings) can be incorporated into the branched skeleton of polycarbosilanes. Cyclic voltammetric analysis suggests that electroreduction of chlorocarbosilanes undergoes an ECE mechanism to initiate polymerization, as well as a myriad of side reactions.