Three unsymmetrical diiodobichalcogenophenes SSeI 2 , STeI 2 , and SeTeI 2 and a diiodoterchalcogenophene SSeTeI 2 were prepared. Grignard metathesis of SSeI 2 , STeI 2 , SeTeI 2 , and SSeTeI 2 occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s- PSSe , PSTe , and PSeTe -through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings ( ca. 1 nm)-from a thiophene unit via a selenophene unit to a tellurophene unit-to form PSSeTe , the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes. Three unsymmetrical diiodobichalcogenophenes SSeI 2 , STeI 2 , and SeTeI 2 and a diiodoterchalcogenophene SSeTeI 2 were prepared to synthesize a new class of polychalcogenophenes with precisely controlled sequences by catalyst-transfer polycondensation.