Poly(dibutylgermylene-co-dihexylgermylene), poly(dibutylsilylene-co-dihexylsilylene), poly(dihexylgermylene-co-dihexylsilylene), poly(dibutylgermylene-co-diphenylgermylene) and poly(methylphenylgermylene-co-dipentylgermylene) were synthesized electrochemically by introducing two corresponding monomers in starting electrolyte solution. The monomer ratio in the copolymers was successfully controlled by changing the ratio of monomers in the starting electrolyte solutions. However, the monomer ratio in the resulting copolymers were different from those in the starting electrolyte solutions. One monomer, which gives a better yield and a higher molecular weight than the other monomer in the homopolymer syntheses, was found in a larger proportion in the copolymer than was expected from the monomer ratio in the starting electrolyte solution. Thermochromic behaviors of the copolymers depended upon the ratio of monomers in the copolymers. It was concluded that random copolymerization was taking place in all the copolymer syntheses studied here.